Leg device for leg type movable robot, and method of controlling leg type movable robot

ABSTRACT

In a foot of a legged mobile robot, deformation of the foot is absorbed by a first concavity and the position and shape of a ground-contact portion hardly change. Accordingly, variation in a resistive force against the moment about the yaw axis can be reduced and a spinning motion can be prevented. In addition, when the foot is placed on a bump or a step, a flexible portion deforms and receives it, and a frictional retaining force is generated between the flexible portion and the bump. Thus, the foot is flexibly adapted to the road surface, and sliding caused by the bump and excessively fast motion are prevented. Accordingly, the foot can be adapted to various kinds of road surfaces such as surfaces having bumps and depressions, and the attitude stability can be increased.

TECHNICAL FIELD

The present invention relates to a legged mobile robot having aplurality of movable legs, and more specifically relates to a structureof a foot which is provided on an end portion of each movable leg andwhich comes into contact with a floor surface (walking surface) during awalking motion. In addition, the present invention also relates to amethod for controlling a legged mobile robot which corresponds to thestructure of the foot.

BACKGROUND ART

In recent years, progress has been made in the research and developmentof legged mobile robots modeled after animals which walk upright on twofeet, such as human beings and apes, and they are increasingly expectedto be used for practical purposes. The legged mobile robots which walkupright on two feet are unstable compared to crawler-type, four-legged,and six-legged robots, and have a disadvantage in that attitude controland walking control thereof are complex. However, they are advantageousin that they can flexibly adapt themselves to places with severeconditions, for example, places where an operational area includes bumpsand depressions as in rough terrains and places with obstacles,discontinuous walking surfaces such as stairs and ladders, etc., andperform locomotion.

Most workspaces and living spaces of human beings are designed inaccordance with their body mechanisms and behavioral patterns that theywalk upright on two feet. As a result, there are so many barriers forpresent mechanical systems using wheels or other driving devices asmoving means to move in living spaces of human beings. In order formechanical systems, that is, robots, to help people with various humantasks or carry out the tasks in place of people and to come intowidespread use in people's living spaces, moving areas of the robots arepreferably the same as those of people. This is the reason why there aregreat expectations of putting the legged mobile robots to practical use.In order to enhance the adaptability of robots to people's livingenvironments, it is necessary that they have a construction similar tothat of human beings.

Various techniques have been proposed with respect to attitude controland stable walking of the legged mobile robots which walk on two feet,and many of them use a zero moment point (ZMP) as a criterion forstability evaluation of walking motion. The stability evaluation usingthe ZMP is based on d'Alembert's principle that a gravity force, aninertial force, and a moment thereof are applied by a walking system toa road surface and this moment is balanced with a ground reaction forceand a ground reaction moment which are applied to the walking system asa reaction from the road surface. As a result of mechanical inference, apoint where moments about a pitch axis and a roll axis are zero existsin a support polygon formed by contact points between the bottom surfaceof a foot and the road surface or on the sides of the support polygon,and this point is called the ZMP.

Biped walking control using the ZMP as a criterion has an advantage inthat positions at which each foot hits the road surface can bedetermined in advance and kinematic constraints on a toe portion of eachfoot corresponding to the shape of the road surface can be easily takeninto account. In addition, when the ZMP is used as a criterion for thestability evaluation, a trajectory, instead of a force, is used as atarget of motion control, and therefore, there is higher technicalfeasibility. The concept of the ZMP and the application thereof as acriterion for the stability evaluation of a walking robot are describedin “Legged Locomotion Robots” written by Miomir kobratovic (“WalkingRobots and Artificial Legs” written by Ichiro Kato et al., published byThe Nikkan Kogyo Shinbun, Ltd.).

The stability and controllability of the legged mobile robots duringlegged motion are affected not only by moving patterns of four limbs butalso by the state of a road surface (ground surface or floor surface) onwhich they perform the legged motion, such as walking. This is becauseas long as a foot is placed on the road surface, it constantly receivesthe reaction force from the road surface. Accordingly, the structure ofthe foot which directly receives the reaction force from the roadsurface is extremely important in view of the stability andcontrollability of the legged mobile robots during the legged motion,and various proposals have been made.

For example, a structure is known in which an elastic sheet composed ofrubber or the like is adhered to the foot bottom surface in order toreduce an impact which occurs when an idling leg (one of the legs whichis separated from the road surface) is placed on the road surface, thatis, an impact in a Z-axis direction (direction perpendicular to the footbottom surface or direction which extends along a yaw axis). Inaddition, a structure in which a metal plate is adhered to the bottomsurface of the elastic sheet in order to prevent the breakage anddeformation of the elastic sheet is also known in the art. In addition,a structure in which a metal plate is provided on the foot bottomsurface with a leaf spring therebetween in order to absorb the impact inthe Z-axis direction and a structure in which a rubber material isapplied to the foot bottom surface in order to prevent slipping on theroad surface are also known in the art.

However, most of the above-described known foot structures are obtainedby making improvements for reducing the impact from the road surfacewhen the foot hits the road surface or preventing slipping on the roadsurface, and the basic shape thereof is not changed from a plate-likeshape, as shown in FIG. 82(A). When a foot 920 shown in FIG. 82 isplaced on a road surface 911, the entire region of the foot bottomsurface is in contact with the road surface 911. In this known foot,when the ZMP is at the central position of the foot 910, as shown inFIG. 82(B), load of the robot may concentrate at this point and the foot910 may deflect away from the road surface 911 and change the shapethereof. In such a case, there is a problem in that the contact areabetween the foot 910 and the road surface 911 decreases and theresistive force against the moment around the yaw axis also decreases.In addition, the shape of a contact surface between the foot sole andthe road surface changes along with the change in the shape of the foot,and this leads to the change in dynamic characteristics of the leggedmobile robot. As a result, the attitude of the robot becomes unstable.

The reduction in the attitude stability is not only caused by thedeflection of the foot sole. Also in the case in which a bump ispositioned under the central area of the foot bottom surface when thefoot sole is placed on the road surface, the foot falls into a so-calledseesaw state and a similar problem occurs.

In addition, since no consideration is made on the corners and sideedges of the foot bottom surface, that is, a ground-contact surface ofthe foot sole, if the road surface has bumps and depressions, thecorners and side edges may interfere with the road surface with bumpsand depressions when the idling leg is placed thereon, and this maycause the robot to stumble. In addition, the robot may fall into aso-called stick-slip state where the robot repeatedly stumbles andrecovers. As a result, the upper body of the robot may loose balance andthe attitude of the robot may become unstable.

As an index of stability of the robot's attitude, a concept referred toherein as “resistive-force-generation effective surface” is used.

When there is only one ground-contact surface between the foot and theroad surface, this surface is defined as the resistive-force-generationeffective surface. In addition, when the foot is in point contact withthe road surface, as shown in FIG. 83, a plane which is surrounded bylines which connect every two adjacent points is defined as theresistive-force-generation effective surface. In addition, when aground-contact portion of the foot is frame-shaped, as shown in FIG. 84,a surface surrounded by the sides of the frame is defined as theresistive-force-generation effective surface. More specifically, the“resistive-force-generation effective surface” corresponds to a surfaceobtained by connecting the points where the resistive force against themoment about the yaw axis generated in the legged mobile robot isapplied by the road surface.

When the ZMP moves as the legged mobile robot walks, the foot deformsand the area of the resistive-force-generation effective surfacedecreases. Accordingly, the resistance against the moment about the yawaxis generated due to the motion of the legged mobile robot decreasesand the attitude of the legged mobile robot becomes unstable. As aresult, spinning motion may occur. In addition, the change in the shapeof the resistive-force-generation effective surface may cause anunexpected change in the behavior of the legged mobile robot, whichleads to the reduction in the attitude stability of the legged mobilerobot.

Accordingly, in the foot bottom surface of the legged mobile robot, boththe static and dynamic adjustments of the surface pressure applied tothe ground-contact surface are necessary. In other words, not only apressure value but also the variation and distribution thereof must beadjusted. In addition, similarly, both the static and dynamicadjustments of friction are necessary.

These problems can be solved if the walking surface is limited to mainlyflat surfaces or smooth, continuous surfaces. However, it is to be notedthat the actual walking surfaces include continuous, swelling surfacesand discontinuous surfaces such as surfaces with bumps and depressionsor steps, and these surfaces are also the cause of the reduction in theattitude stability of the legged mobile robots.

More specifically, when a foot is placed on a step, as shown in FIG. 85,the foot totters and support moment cannot be generated at aground-contact portion. As a result, the behavior of the foot becomesnonlinear and its control becomes extremely difficult. In addition, themotion trajectory becomes unstable, and correction control and amovement plan must be reset.

In addition, when the foot is placed on a delicate, slippery surface,such as a carpet, as shown in FIG. 86, there is a high possibility thatthe ground-contact surface of the foot will slip and the motionstability of the legged mobile robot will decrease considerably.

In addition, when the foot is placed on a surface with high friction ora soft surface which easily catches the foot, as shown in FIG. 87,falling moment is generated due to the inertial force, etc., when thesurface pressure, which depends on the shape of the ground-contactsurface of the foot, or friction in the planar direction excessivelyincreases. Therefore, it is necessary to adjust the frictionalcharacteristics of the ground-contact portion.

In addition, when the foot is placed on a step, as shown in FIG. 88, inaddition to the problem of the support moment described above withreference to FIG. 85, there is also a problem in that the foot may slidedown when conditions of the shape of the step, or a bump, are not goodor when the friction is extremely low. In addition, since such a motionis extremely fast compared to control cycles, there is a risk thatsuitable countermeasures cannot be implemented.

In such a case, as shown in FIG. 89, a structure like a plantar arch,for example, may be formed in the foot so as to avoid the edge of thestep. However, in this structure, the plantar arch comes into contactwith the edge of the step or the bump such that aresistive-force-generation effective surface 921 has a triangular shape,as shown by the hatched area in the figure, and conditions for ensuringthe stability become severe. The motion performance and the stabilitymust also be ensured on the steps.

In addition, with respect to biped walking robots, there is always apossibility of falling over, which must be avoided as much as possible.In order to avoid falling over, the development of control methods iscarried out in view of how to avoid the disturbance of the balance andachieve stable motion and how to recover after losing the balance. Inaddition to the development of control methods, foot structures shown inFIGS. 90 to 92 are used.

FIGS. 90 to 92 are plan views showing schematic constructions of knownfeet. In the figures, each of reference numerals 12, 22, and 32 denotesa side surface (outer side surface) which is remote from the other foot(foot which is attached to a leg which forms a pair with a leg on whichthe foot shown in each figure is attached). In addition, each ofreference numerals 13, 23, and 33 denotes a side surface (inner sidesurface) which is adjacent to the other foot; each of reference numerals14, 24, and 34 denotes a side surface at the front of the robot; andeach of reference numerals 15, 25, and 35 denotes a side surface at therear of the robot. In addition, each of reference numerals 11, 21, and31 denotes an attachment for attaching the foot on an ankle of thecorresponding leg of the robot.

In the foot shown in FIG. 90, the outer side surface 12 is curvedoutward. In addition, in the foot shown in FIG. 91, the outer sidesurface 22 includes two planar surfaces such that the outer side surface22 projects outward, and a vertex 26 is formed on a line where the twoplanar surfaces intersect. In addition, in the foot shown in FIG. 92,projections 36 and 37 are formed on the outer side surface 32 and theinner side surface 33, respectively, at the central positions thereof.The purpose of forming the outer side surfaces 12, 22, and 32 such thatthey project outward, as shown in the figures, is to improve thestability of the robot with respect to the outward (direction away fromthe other foot) rotation.

In FIGS. 90 and 91, in addition to the outer side surfaces 12 and 22,the inner side surfaces 13 and 23 may also project outward in a mannersimilar to the outer side surfaces 12 and 22, respectively.

In the above-described known foot structures, since the outer sidesurface of each foot projects outward, it can be assumed that thestability with respect to the leftward and rightward rotational momentof the robot is increased in a state before falling motion starts.

However, if the foot is constructed as shown in FIG. 90, once thefalling motion starts and the robot is somewhat tilted outward (to theleft or right), the contact area between the outer edge (edge betweenthe outer side surface and the bottom surface) and the road surface isgradually shifted. More specifically, the foot starts to roll along thecurve of the outer edge. In addition, if the foot is constructed asshown in FIGS. 91 or 92, the outer edge of the foot comes into pointcontact with the road surface at a single projecting point (the vertex26 or a corner of the projection 36). Therefore, rotating motion aroundthe yaw axis (axis which is perpendicular to the foot bottom surface)centered on the contact point occurs depending on the position of thegravity center of the robot in the falling motion. Generally, it isextremely difficult to predict how this rotating motion occurs.

As described above, in the known foot structures, the attitude of therobot in the falling motion is not constant, and is difficult topredict. Therefore, once the falling motion starts, it is difficult toimplement controls related to the falling motion, for example, controlto avoid falling over, control to reduce the impact of falling over,control to recover from falling over, etc. Accordingly, the robot cannothelp but fall over, and it is difficult to cause the robot to recover byitself.

In addition, since the falling motion is not constant, in order toprevent the breakage of each part of the robot due to collision with theroad surface when the robot falls over, it is necessary to increase therigidity and the impact resistance of all of the parts which may collidewith the road surface. Accordingly, there is a problem in that the costof the robot increases.

In addition, the legged mobile robots are currently moving from theresearch stage to practical application, and there are still manytechnical problems which must be solved. For example, although the stateof the road surface (whether or not it is rough, the coefficient offriction thereof, etc.) has a large influence on the attitude stabilitycontrol in legged walking motion and stable walking, this is not fullyunderstood. In addition, in biped walking robots such as humanoids, thegravity center is at a higher position and the stability region of ZMPduring walking is smaller compared to four-legged walking robots.Therefore, the problem of attitude variation depending on the state ofthe road surface is particularly important for the biped walking robots.

When the walking motion on a road surface is considered, a walkingmethod suitable for the state of the road surface is preferably used.Japanese Patent Application No. 2000-100708, which has been assigned tothe present applicant, discloses a legged mobile robot which can performsuitable legged locomotion in accordance with the state of the roadsurface. In the legged mobile robot according to this publication, asurface contact sensor for determining the state of contact between afoot and a road surface and a relative-movement measurement sensor formeasuring the relative movement (that is, slipping) between the roadsurface and the leg placed on the road surface are provided on the foot(plantar or sole) of each movable leg. Even when, for example, slippingoccurs and the actual trajectory is shifted from a planned or scheduledtrajectory, correction of a movement plan and motion control can beperformed adaptively.

In addition, when walking motion of human beings is considered, walkingmotion on a normal road surface and that on a slippery road surface,such as a snowy road surface, are generally different from each other.In addition, walking motion on a wooden floor and that on a thick carpetare also different from each other. Human beings walk in accordance withthe state of the road surface while observing the situation with fivesenses, selecting how to walk from among experimentally-learned walkingmethods, and performing attitude control in accordance with on thesituation. In addition, human beings select shoes or the like which aresuitable for the road surface on which they walk, and thereby easilyadapt themselves to extreme road conditions such as snowy roads and dirtroads.

With respect to the walking stability of the robots, although the robotsare required to walk on various kinds of road surfaces similarly tohuman beings, it is difficult for the robots to perform various walkingmotions similarly to human beings.

On the other hand, with respect to the relationship between the robotsand the road surface, when the size and the weight of the robots aresimilar to those of human beings, it can be assumed that the influenceof the road surface on the walking state of the robots is similar tothat on the walking state of human beings.

In comparison, when the size and the weight of the robots are less thanthose of human beings, the influence of the state of the road surfacemay increase. As an example, a road surface which deforms when load isapplied, such as a carpet, will be described below. When a human beingwalks on a carpet, even when the carpet is thick, the surface of thecarpet is pressed at a region where a foot is placed and the roadsurface becomes stable since his or her weight is sufficiently large. Inaddition, the reaction force from fibers of the carpet has only a smallinfluence on the walking motion. In comparison, when a small, lightrobot walks on the same carpet, a pressure applied to the surface of thecarpet by a foot sole of the robot is small, and the surface of thecarpet cannot be sufficiently pressed at a region where the foot isplaced. As a result, a situation similar to that when a human beingwalks on a thick mattress occurs and the walking motion is largelyinfluenced.

It is difficult for the robots to perform various walking patterns likehuman beings, and the robots cannot easily adapt themselves to the roadsurface on which they are walking. In addition, the robots and humanbeings receive different kinds of influences from the road surface.

Although the foot and the foot sole of the robots are widely researchedand developed, it is currently difficult to obtain a perfect foot whichcan be adapted to any type of road surface from a both technical andfinancial point of view.

In addition, the legged mobile robots are still in the research anddevelopment stage, and their development mainly aims to increase theadaptability of the robot's foot in work environments where the roadsurface is limited.

Accordingly, as the legged mobile robots are transferred to practicalapplication and product development to be used in people's livingspaces, it is necessary to adapt them to various states of roadsurfaces.

In view of the above-described situation, the present applicant hasproposed a legged mobile robot having a foot which can be replacedaccording to the state of the road surface in Japanese PatentApplication No. 2000-167681.

In addition, the present applicant has also proposed a legged mobilerobot having a foot which has a two-part structure including an instepwhich is connected to an ankle and a foot sole which is detachablyattached to the instep such that it comes into contact with the roadsurface (Japanese Patent Application No. 2002-037997). In thisstructure, the foot sole can be replaced according to the state of theroad surface. Since only the foot sole, which contributes most to theadaptation to the state of the road surface and which is worn most bycoming into contact with the road surface, is replaced, many kinds offoot soles suitable for various states of road surfaces can be preparedat a low cost compared to the case in which the entire foot is replaced.

In addition, when a foot or a foot sole of a legged mobile robot isreplaced, settings for suitable foot motion, ZMP trajectory, trunkmotion, upper limb motion, and height of hips change. Accordingly, it isnecessary to change these settings. In order to suitably change thesesettings, information such as the shape of the foot or the foot sole,the coefficient of friction, and the weight of the foot or the foot solemust be provided to a main controller of the robot's main body. In thiscase, a method may be used in which the information related to the footor the foot sole is stored in a ROM mounted in the robot's main body anda user inputs information for identifying the new foot or foot sole.

However, in this method, information corresponding to all of the feet orthe foot soles to be replaced must be stored in the ROM. Thus, if anextremely large number of feet or foot soles are prepared, the number ofROMs or the capacity of the ROM must be increased accordingly. Thisleads to a difficult problem if a sufficiently large space cannot beprovided for accommodating the ROMs as in small legged mobile robots,and high costs are incurred if a large-capacity ROM is used. Inaddition, it is cumbersome for the user to input the above-describedidentification information each time the foot or the foot sole isreplaced.

In addition, in the above-described known foot structures, although theimpact in the Z-axis direction applied to the foot sole by the roadsurface when the foot sole is place on the road surface can be somewhatabsorbed with the elastic sheet or the leaf spring, a force applied in aspecific or unspecific direction along a plane perpendicular to theZ-axis direction (X-Y plane) is not taken into account. Morespecifically, when the road surface has bumps and depressions, a part ofthe foot may interfere with the surface with bumps and depressions (becaught by the surface or stumble thereon) when an idling leg is placedon the road surface, and there is a risk that the upper body of therobot will lose balance and the attitude thereof will become unstable.This problem becomes more severe when a high-speed motion is performedsince the reaction force from the road surface increases. In such acase, the robot takes an emergency avoidance motion based on a softwareprocess performed by control means of the robot. However, it isadvantageous in view of stability control and walking control if thisproblem can be avoided or eased with a hardware structure of the foot.

In addition, the foot is provided with various sensors for detectingbasic information used by the main controller of the robot's main bodyto control the motion of each part, such as movable legs. For example,when the motion control of the robot is performed by using the ZMP asthe criterion for stability evaluation, a plurality of force sensors forZMP detection are disposed on the foot bottom surface (surface whichcomes into contact with the road surface) in order to measure the actualZMP. In addition, the foot may also be provided with, for example,sensors for determining whether or not the foot is placed on the roadsurface, sensors for determining whether or not the foot placed on theroad surface is slipping on the road surface, etc.

The detection values obtained by the sensors are A/D converted and areinput to a main controller of the robot's main body. Then, the maincontroller calculates the actual ZMP on the basis of the detectionvalues and performs other calculation processes, and controls the motionof each part, such as the walking motion, on the basis of thecalculation results.

However, since the main controller of the robot's main body directlyreceives the outputs from the sensors mounted on the foot and performsnecessary calculation processes including the ZMP calculation, there isa problem in that a large processing load is placed on the maincontroller. More specifically, a computing unit of the main controllerwhich is mounted in the robot's main body performs complex and enormouscalculations for, for example, setting the motion of the robot.Accordingly, if the computing unit of the main controller must calculatethe actual ZMP on the basis of the outputs from the above-described ZMPdetection sensors and process outputs from other sensors, a largecalculation load is placed on the computing unit of the main controller.

In addition, in order to supply the outputs from the sensors provided oneach foot to the main controller of the robot's main body, complexwiring is necessary to connect the sensors and the main controller.Furthermore, when the foot is replaced, it may be necessary to changethe wiring in the robot's main body if the kind, the characteristics,the number, etc., of the sensors provided on the foot are changed. Insuch a case, there is a problem in that a large workload is required forreplacing the foot.

DISCLOSURE OF INVENTION

In view of the above-described problems, a main object of the presentinvention is to provide a foot of a legged mobile robot in which thevariation in a resistive-force-generation effective surface caused bythe variation in the shape of the foot due to the movement of the ZMP isreduced, which is adaptable to various walking surfaces such ascontinuous and discontinuous surfaces, rigid surfaces, viscoelasticsurfaces, etc., and which ensures sufficient attitude stability of therobot.

In addition, another object of the present invention is to provide alegged mobile robot in which the variation in theresistive-force-generation effective surface caused by the variation inthe shape of the foot due to the movement of the ZMP is reduced, whichhas a foot adaptable to various walking surfaces such as continuous anddiscontinuous surfaces, rigid surfaces, viscoelastic surfaces, etc., andwhich thereby ensures sufficient attitude stability.

In addition, another object of the present invention is to provide astructure of a foot with which the behavior of a robot when it fallsover can be predicted, controls related to the falling motion, forexample, control to avoid falling over, control to reduce the impact offalling over, control to recover from falling over, etc., can be easilyimplemented, and the breakage of each part due to falling can beprevented.

In addition, another object of the present invention is to facilitatethe process in which a control system of the robot's main body acquiresinformation related to a new foot or sole when an old one is replacedtherewith, so that a workload required when the foot or the foot sole isreplaced can be reduced.

In addition, another object of the present invention is to provide alegged mobile robot which can perform high-speed motion with highstability and a foot of the legged mobile robot.

In addition, another object of the present invention is to reduce aprocessing load placed on control means of the robot's main body, toprevent the complication of wiring for connecting the sensors providedon the foot and the control means of the robot's main body, and tofacilitate the process of replacing the foot.

According to one aspect of the present invention, a foot of a leggedmobile robot having a plurality of movable legs includes a firstconcavity formed in a ground-contact surface of the foot at a centralarea of the ground-contact surface and a flexible portion with apredetermined elasticity which is disposed in the first concavity.

Preferably, the flexible portion is composed of an elastic materialhaving a predetermined elasticity or a viscous material having apredetermined viscosity. In addition, preferably, the flexible portionis composed of a material having hysteresis characteristics with respectto deformation.

In addition, preferably, the flexible portion does not come into contactwith a road surface when the foot is placed thereon if the road surfaceis flat. In addition, preferably, the flexible portion covers the innersurface of the first concavity.

In the foot of the legged mobile robot having the above-describedconstruction, even when the ZMP is at the central position of the footand deflection of the foot around this position occurs, the deformationcan be absorbed by a concavity including the first concavity and theposition and the shape of a ground-contact portion hardly change.Accordingly, variation in the resistive force against the moment aboutthe yaw axis can be reduced and so-called spinning motion can beprevented. In addition, motion of the legged mobile robot can bepredicted and be suitably controlled by a control system, and theattitude of the legged mobile robot can be maintained stable.

In addition, when the foot is placed on a bump or a step, the bump,etc., comes into contact with the flexible portion disposed in the firstconcavity. Accordingly, the shape of the flexible portion changes so asto match the shape of the bump, and friction is generated between thebump and the flexible portion in that state. Thus, the foot is flexiblyadapted to the road surface. As a result, the bump functions as if it isa part of the foot, and dangerous motions in view of control such assliding and excessively fast motion can be prevented.

Preferably, a ground-contact portion which actually comes into contactwith the road surface if the road surface is flat is provided at apredetermined position in a peripheral area of the foot, and the firstconcavity is formed in, for example, a dome shape at an area surroundedby the -ground-contact portion.

In addition, preferably, the first concavity is formed such that itextends through the foot in a direction perpendicular to the walkingdirection at a central position of the foot in the walking direction.

In addition, preferably, the ground-contact portion and side surfaces ofthe foot are connected to each other with smooth curved surfaces. Morespecifically, peripheral portions around the ground-contact area, thatis, connecting parts between the ground-contact portion and the sidesurfaces of the foot, are preferably formed as smooth curved surfaces.

According to the above-described construction, even when there are bumpsand depressions on the road surface, the peripheral portions can beprevented from interfering with the road surface and the foot can beprevented from being caught by the road surface or stumbling.Accordingly, the robot can be prevented from falling into a so-calledstick-slip state, and stable attitude control of the robot can beperformed continuously.

In addition, preferably, the foot further includes a second concavity inthe first concavity, the second concavity being deeper than the firstconcavity, and the flexible portion is disposed in the second concavity.

Preferably, the first concavity has slopes which extend from theground-contact portion such that the slopes are separated from the roadsurface, and the second concavity is deeper than the slopes of the firstconcavity.

In addition, preferably, the flexible portion covers at least theceiling surface of the second concavity.

In the foot of the legged mobile robot having the above-describedconstruction, when the foot is placed on a bump such as a step, the bumpis received not only by the first concavity but also by the secondconcavity. Accordingly, the risk of falling into an unstable statecalled a seesaw state can be reduced.

In addition, if the bump comes into contact with the flexible portiondisposed in the second concavity when the foot is placed on the bump,the flexible portion deforms and enwraps the bump. Accordingly, theflexible portion retains the bump by friction, and the foot is flexiblyadapted to the road surface. As a result, sliding or excessively fastmotion can be prevented.

In addition, preferably, the second concavity is formed such that itextends through the foot in a direction perpendicular to the walkingdirection at a central position of the foot in the walking direction.More specifically, the second concavity is preferably formed like aplantar arch of a human foot.

In such a case, side surfaces of the second concavity which extendsthrough the foot preferably have shapes with smooth curved lines orlinear lines on a plane parallel to the ground-contact surface. Morespecifically, boundary regions in front of and behind the plantar-archportion preferably have continuous shapes with curved lines or linearlines such that discontinuous portions which have a risk of being caughtby the road surface are not provided.

In addition, preferably, the side surfaces of the second concavity andthe slopes of the first concavity are connected to each otherdiscontinuously. More specifically, the side surfaces of the secondconcavity are not connected to the slopes of the first concavity withsmooth curved surfaces but are connected with substantiallydiscontinuous bent portions at positions separated from the roadsurface.

In addition, preferably, the side surfaces of the second concavity areapproximately parallel to a direction perpendicular to theground-contact surface, that is, the vertical direction, and theinclination thereof is closer to vertical than the slopes of the firstconcavity. Preferably, the second concavity has a columnar shape.

In the above-described construction, when, for example, the leggedmobile robot walks on a carpet, fibers of the carpet enter the secondconcavity and come into contact with the flexible portion disposed inthe second edge and receive a relatively large frictional force. Inaddition, the fibers encounter a side surface of the second concavitywhich is approximately perpendicular to the moving direction of thefibers, and are caught by the edge of the side surface of the secondconcavity. Accordingly, resistive force and reaction force are appliedto the fibers of the carpet. These forces applied to the fibers of thecarpet, which is the walking surface, serve to prevent slipping in boththe walking direction and the direction opposite thereto. As a result,even when the legged mobile robot walks on a slippery carpet, a suitablefrictional force can be applied to the foot and a suitable impellingforce can be obtained during walking.

In addition, a legged mobile robot according to the present inventionincludes a plurality of movable legs and a foot which is provided on anend portion of each of the movable legs. The foot includes a firstconcavity formed in a ground-contact surface of the foot at a centralarea of the ground-contact surface and a flexible portion with apredetermined elasticity which is disposed in the first concavity.

In addition, according to another aspect of the present invention, afoot of a legged mobile robot having a plurality of movable legsincludes a first concavity formed in a ground-contact surface of thefoot at a central area of the ground-contact surface, the firstconcavity being, for example, dome-shaped, and one or more grooves whichare formed, each groove being formed in the ground-contact surface ofthe foot such that the groove extends from the first concavity across aperipheral portion of the foot and communicates with the outside throughone of side surfaces of the foot.

In the foot of the legged mobile robot having the above-describedconstruction, even when the ZMP is at the central position of the footand deflection of the foot around this position occurs, the deformationcan be absorbed by a concavity including the first concavity and theposition and the shape of a ground-contact portion hardly change.Accordingly, variation in the resistive force against the moment aboutthe yaw axis can be reduced and spinning motion can be prevented. Inaddition, motion of the legged mobile robot can be predicted and besuitably controlled by a control system, and the attitude of the leggedmobile robot can be maintained stable.

Preferably, the foot of the legged mobile robot according to the presentinvention includes a plurality of ground-contact portions disposed on aground-contact surface of the foot at predetermined positions in theperipheral area of the ground-contact surface, and one of more groovesare formed such that they extend between the adjacent ground-contactportions.

In addition, preferably, four grooves are formed such that they extendfrom the first concavity to four sides of the foot, that is, the frontside of the foot in the walking direction, the rear side of the foot inthe walking direction, and the left and right sides of the foot withrespect to the walking direction.

Preferably, side surfaces of the grooves have shapes with nonlinearcurves on a plane parallel to the ground-contact surface, and a suitablefrictional force is generated when, for example, fibers of a carpet comeinto contact with the side surfaces of the grooves. For example, thewidths of the grooves preferably decrease toward the sides of the foot,so that the fibers are forcibly moved such that the contact resistanceincreases.

In addition, parts of the side surfaces of the grooves are preferablyformed of smooth curved surfaces so that they can be prevented frombeing caught by the road surface, etc.

In addition, preferably, the ground-contact portions and the sidesurfaces of the foot are connected to each other with smooth curvedsurfaces. More specifically, peripheral portions around theground-contact surfaces, that is, connecting parts between theground-contact portions and the side surfaces of the foot, arepreferably formed as smooth curved surfaces.

According to the above-described construction, when there are bumps anddepressions on the road surface, the peripheral portions can beprevented from interfering with the road surface and the foot can beprevented from being caught by the road surface or stumbling.Accordingly, the robot can be prevented from falling into a so-calledstick-slip state, and stable attitude control of the robot can beperformed continuously.

In addition, preferably, the foot further includes a second concavity inthe first concavity, the second concavity being deeper than the firstconcavity. For example, the first concavity has a slope which extendsfrom the ground-contact portion such that the slope is separated fromthe road surface, and the second concavity is deeper than the slope ofthe first concavity.

In the foot of the legged mobile robot having the above-describedconstruction, when the foot is placed on a bump such as a step, the bumpis received not only by the first concavity but also by the secondconcavity. Accordingly, the risk of falling into an unstable statecalled a seesaw state can be reduced.

In addition, preferably, a side surface of the second concavity and theslope of the first concavity are connected to each otherdiscontinuously. More specifically, the side surface of the secondconcavity is not connected to the slope of the first concavity with asmooth curved surface but is connected with a substantiallydiscontinuous bent portion at a position separated from the roadsurface.

In addition, preferably, the side surface of the second concavity isapproximately parallel to a direction perpendicular to theground-contact surface, that is, the vertical direction, and theinclination thereof is closer to vertical than the slope of the firstconcavity. The second concavity has, for example, a columnar shape.

In the above-described construction, when, for example, the leggedmobile robot walks on a carpet, fibers of the carpet enter the secondconcavity and come into contact with a flexible portion disposed in thesecond edge and receive a relatively large frictional force. Inaddition, the fibers encounter the side surface of the second concavitywhich is approximately perpendicular to the moving direction of thefibers, and are caught by the edge of the side surface of the secondconcavity. Accordingly, resistive force and reaction force are appliedto the fibers of the carpet. These forces applied to the fibers of thecarpet, which is the walking surface, serve to prevent slipping in boththe walking direction and the direction opposite thereto. As a result,even when the legged mobile robot walks on a slippery carpet, a suitablefrictional force can be applied to the foot and a suitable impellingforce can be obtained during walking.

In addition, preferably, a flexible portion having a predeterminedelasticity is disposed in the first concavity or in the secondconcavity. The flexible portion is preferably composed of an elasticmaterial having a predetermined elasticity or a viscous material havinga predetermined viscosity. In addition, preferably, the flexible portionis composed of a material having hysteresis characteristics with respectto deformation.

In addition, preferably, the flexible portion does not come into contactwith the road surface when the foot is placed thereon if the roadsurface is flat. For example, the flexible portion covers the innersurface of the first concavity, or at least the ceiling surface of thesecond concavity.

In the foot of the legged mobile robot having the above-describedconstruction, when the foot is placed on a bump or a step, the bump,etc., comes into contact with the flexible portion disposed in the firstconcavity or the second concavity. Accordingly, the shape of theflexible portion changes so as to match the shape of the bump, andfriction is generated between the bump and the flexible portion in thatstate. Thus, the foot is flexibly adapted to the road surface. As aresult, the bump functions as if it is a part of the foot, and dangerousmotions in view of control such as sliding and excessively fast motioncan be prevented.

In addition, a legged mobile robot according to the present inventionincludes a plurality of movable legs and a foot which is provided on anend portion of each of the movable legs. The foot includes a firstconcavity formed in a ground-contact surface of the foot at a centralarea of the ground-contact surface and one or more grooves, each groovebeing formed in the ground-contact surface of the foot such that thegroove extends from the first concavity across a peripheral portion ofthe foot and communicates with the outside through one of side surfacesof the foot.

In addition, according to another aspect of the present invention, afoot of a legged mobile robot includes a ground-contact portion disposedon a ground-contact surface of the foot at a predetermined position in aperipheral area of the ground-contact surface, a first concavity formedin the ground-contact surface of the foot at an area surrounded by theground-contact portion, the first concavity having a slope which extendsfrom the ground-contact portion such that the slope is separated fromthe road surface, and a second concavity in the first concavity, thesecond concavity being deeper than the slope of the first concavity.Preferably, the first concavity is dome-shaped and the second concavityis column-shaped. More specifically, the second concavity is formed as,for example, a recess of a circular column shape.

In the foot of the legged mobile robot having the above-describedconstruction, even when the ZMP is at the central position of the footand deflection of the foot around this position occurs, the deformationcan be absorbed by a concavity including the first concavity and thesecond concavity and the position and the shape of the ground-contactportion hardly change. Accordingly, variation in the resistive forceagainst the moment about the yaw axis can be reduced and spinning motioncan be prevented. In addition, motion of the legged mobile robot can bepredicted and be suitably controlled by a control system, and theattitude of the legged mobile robot can be maintained stable.

In addition, when the foot is placed on a bump such as a step, the bumpis received by the concavity including the first concavity and thesecond concavity. Accordingly, the risk of falling into an unstablestate called a seesaw state can be reduced.

In addition, preferably, a side surface of the second concavity isapproximately parallel to a direction perpendicular to theground-contact surface, that is, the vertical direction, and theinclination thereof is closer to vertical than the slope of the firstconcavity.

In addition, the side surface of the second concavity and the slope ofthe first concavity are preferably connected to each otherdiscontinuously. More specifically, the side surface of the secondconcavity may also be formed such that it is not connected to the slopeof the first concavity with a smooth curved surface but is connectedwith a substantially discontinuous bent portion at a position separatedfrom the road surface due to the inclination of the slope of the firstconcavity.

According to the above-described construction, when, for example, thelegged mobile robot walks on a carpet, fibers of the carpet enter thesecond concavity and encounter the side surface of the second concavityor are caught by the side surface of the second concavity. The surfaceencountered by the fibers are approximately perpendicular to thedirection in which the fibers encounters this surface, and force cannotbe dispersed as in the case in which this surface is a continuoussurface such as a slope and a curved surface. Accordingly, resistiveforce and reaction force are applied to the fibers of the carpet by theside surface and the edge of the second concavity encountered by thefibers of the carpet. These forces applied to the fibers of the carpet,which is the walking surface, serve to prevent slipping in both thewalking direction and the direction opposite thereto. As a result, evenwhen the legged mobile robot walks on a slippery carpet, a suitablefrictional force can be applied to the foot and a suitable impellingforce can be obtained during walking. In addition, the second concavityis formed such that it extends through the foot in a directionperpendicular to the walking direction at a central position of the footin the walking direction. More specifically, the second concavity ispreferably formed like a plantar arch of a human foot. In such a case,side surfaces of the second concavity which extends through the footpreferably have shapes with smooth curved lines or linear lines on aplane parallel to the ground-contact surface. More specifically,boundary regions in front of and behind the plantar-arch portionpreferably have continuous shapes with curved lines or linear lines suchthat discontinuous portions which have a risk of being caught by theroad surface are not provided.

In addition, preferably, the ground-contact portion and side surfaces ofthe foot are connected to each other with smooth curved surfaces. Morespecifically, peripheral portions around the ground-contact area, thatis, connecting parts between the ground-contact portion and the sidesurfaces of the foot, are preferably formed as smooth curved surfaces.According to this construction, even when there are bumps anddepressions on the road surface, the peripheral portions can beprevented from interfering with the road surface and the foot can beprevented from being caught by the road surface or stumbling.Accordingly, the robot can be prevented from falling into a so-calledstick-slip state, and stable attitude control of the robot can beperformed continuously.

In addition, a legged mobile robot according to the present inventionincludes a plurality of movable legs and a foot which is provided on anend portion of each of the movable legs. The foot includes aground-contact portion disposed on a ground-contact surface of the footat a predetermined position in a peripheral area of the ground-contactsurface, a first concavity formed in the ground-contact surface of thefoot at an area surrounded by the ground-contact portion, the firstconcavity having a slope which extends from the ground-contact portionsuch that the slope is separated from the road surface, and a secondconcavity in the first concavity, the second concavity being deeper thanthe slope of the first concavity.

In addition, according to another aspect of the present invention, alegged mobile robot includes a plurality of movable legs and a footprovided on each of the movable legs. The foot includes a foot solehaving a foot bottom surface and side surfaces which extend continuouslyfrom the periphery of the foot bottom, the foot sole including aplantar-arch portion having a slope which slopes toward the inside ofthe foot bottom surface.

According to the present invention, the plantar-arch portion having aslope which slopes toward the inside of the foot bottom surface isprovided, and a ground-contact portion which comes into contact with theroad surface is disposed around the plantar-arch portion. Accordingly,even when the ZMP is at the central position of the foot sole anddeflection of the foot sole around this position occurs, the deformationcan be absorbed by the plantar-arch portion and the position and theshape of the ground-contact portion hardly change. Accordingly,variation in the resistive force against the moment about the yaw axiscan be reduced and so-called spinning motion can be prevented. Inaddition, motion of the legged mobile robot controlled by a controlsystem can be predicted, and the attitude stability can be improved.

In addition, since the plantar-arch portion is provided, even if thecentral area of the foot bottom surface is positioned above a bump onthe road surface when the foot sole is placed on the road surface, thepossibility that the foot will step on the bump can be reduced.Accordingly, the possibility that the foot will fall into a so-calledseesaw state can be reduced.

Preferably, the foot bottom surface and the side surfaces of the footsole are connected to each other with smooth curved surfaces. In such acase, since the corners and the side edges of the foot sole are formedof smooth curved surfaces, even when there are bumps and depressions onthe road surface, the corners and the side edges can be prevented frominterfering with the road surface and the foot can be prevented frombeing caught by the road surface or stumbling. Accordingly, the robotcan be prevented from falling into a stick-slip state, and the stabilityof the robot's attitude can be improved. The plantar-arch portion has atapered surface which extends continuously from the ground-contactportion, and may be domed-shaped or cone-shaped.

In addition, although the shape of the foot sole is not particularlylimited, it may be rectangular shaped or rectangular-plate shaped.Although a foot structure is known in which the periphery of a foot soleis curved, for example, a side edge of the foot sole is curved toproject outward, when this structure is used, there is a risk in thatthe foot will roll along the curved side and the attitude stability ofthe robot will be reduced when the robot is tilted toward this side. Incomparison, when the bottom shape of the foot sole is rectangular, thatis, when the side edges of the foot sole are linear, the rolling motioncan be prevented.

In addition, the ground-contact portion is preferably disposed at eachof four corners of the foot bottom surface. By increasing the distancesbetween the ground-contact portions, the resistive force against themoment about the yaw axis can be increased and the attitude stability ofthe robot can be improved.

In addition, according to another aspect of the present invention, alegged mobile robot includes a pair of movable legs and a foot which isattached to an end portion of each of the movable legs. The footincludes a foot sole having a rectangular foot bottom surface whichcomes into contact with a road surface and a plurality of side surfaceswhich extend continuously from side edges of the foot bottom surface.The shape of one of the side surfaces corresponding to an outer sideedge of the foot bottom surface which is remote from the other foot isset such that the shape of the outer side edge is a substantially linearline when the outer side edge is projected onto a plane including thefoot bottom surface. In the description above, “substantially linearline” is not necessarily an exactly linear line from a geometric pointof view, and includes any line which can be considered as linear withrespect to the road surface.

According to the present invention, when, for example, the robot losesits balance to the left or right and the foot placed on the road surfacerotates around the outer side edge, the entire region of the outer edgeis in line contact with the road surface. Accordingly, the robot rotatesoutward around the outer side edge without causing the rotation aroundthe yaw axis of the foot sole (axis perpendicular to the foot bottomsurface).

Alternatively, the foot attached to the end portion of each of themovable legs includes a foot sole having a polygonal bottom surfacewhich comes into contact with a road surface and a plurality of sidesurfaces which extend continuously from side edges of the foot bottomsurface. The shape of at least one of the side surfaces is set such thatthe shape of the corresponding side edge is an inwardly curved line whenthe side edge is projected onto a plane including the foot bottomsurface.

For example, the shape of one of the side surfaces corresponding to anouter side edge of the foot bottom surface (side edge which is remotefrom the other foot) is set such that the shape of the outer side edgeis an inwardly curved line when the outer side edge is projected onto aplane including the bottom surface. In such a case, when, for example,the robot loses its balance to the left or right and the foot placed onthe road surface rotates around the outer side edge, only two points atthe front and rear of the outer side edge which project most are incontact with the road surface. Accordingly, the robot rotates outwardaround an imaginary line which connects the two points without causingthe rotation around the yaw axis of the foot sole (axis perpendicular tothe foot bottom surface). This also applies to other side edges.

When the above-described foot structure is used, the attitude andbehavior of the robot when it falls over can be predicted to someextent. Accordingly, controls related to the falling motion such ascontrol to avoid falling over (for example, control to recover thebalance by suitably moving the gravity center), control to reduce theimpact of falling over (for example, control to place a hand of therobot on the road surface to prevent the robot's body from directlycolliding with the road surface), and control to recover after fallingover (for example, control to stand up from the fallen state), can beeasily implemented. In addition, since the robot falls over around apredetermined line without causing the rotation around the yaw axis, itis only necessary that parts on the sides of the robot which areexpected to collide with the road surface first be provided withanti-impact measures (for example, the corresponding parts may beconstructed such that they have high-rigidity or impact-resistantstructure or buffers such as cushions may be provided on thecorresponding parts). Accordingly, the costs can be reduced.

In addition, notches may be formed in the side surfaces at the centralpositions of the side surfaces. If there is a small bump or an obstacleon the road surface when the robot falls over, there is a risk in thatthe foot will step on the obstacle, etc., and the above-described statein which the outer side edge is in line contact or two-point contactwith the road surface cannot be obtained. However, when the notches areformed in the side surfaces, the foot can be prevented from stepping ona small bump or an obstacle and unexpected change in the attitude andbehavior of the robot in the falling motion can be reduced.

In addition, according to another aspect of the present invention, alegged mobile robot includes a movable leg and a foot which is providedon an end portion the movable leg. The foot includes a main foot bodywhich is detachably attached to an end portion the movable leg andmemory means which is provided on the main foot body and which storesinformation related to the main foot body.

Alternatively, the foot includes a main foot body which is detachablyattached to an end portion of the movable leg, memory means which isprovided on the main foot body and which stores information related tothe main foot body, and control means which controls the motion of themovable leg on the basis of the information stored in the memory means.In this case, the control means may read out the information stored inthe memory means at the time of initialization. The time ofinitialization is the time when the power of the robot is turned on,when the robot is reset, or when the main foot body is attached to themovable leg.

In addition, a method for controlling a legged mobile robot having theabove-described construction includes the steps of storing informationrelated to the foot in memory means provided on the foot; reading outthe information from the memory means at the time of initialization; andcontrolling motion of the movable leg on the basis of the informationread out.

In addition, a foot of a legged mobile robot may include an instep whichis attached to an end portion of the movable leg, a foot sole detachablyattached to the instep, memory means which is provided on the foot soleand which stores information related to the foot sole, and read-outmeans which is provided on the instep and which reads out theinformation stored in the memory means.

In addition, in order to reduce the interference of the foot with theroad surface and improve the attitude stability, the foot sole ispreferably attached to the instep in a movable manner. In such a case,buffer means or urging means for reducing the impact transmitted to theinstep due to the movement of the foot sole is preferably providedbetween the foot sole and the instep.

In addition, the foot sole may be attached to the instep by fasteningmeans with variable fastening conditions.

According to the present invention, since the memory means which storesthe information related to the foot is provided on the foot (main footbody or foot sole), a main control system of the robot's main body whichcontrols the motion of the movable leg can read out the informationstored in the memory means and control the motion of the movable leg onthe basis of information including the information read out.Accordingly, it is not necessary to input the information related to thefoot into a memory included in the main control system of the robot, andthe task of replacing the foot can be facilitated. In addition, it isnot necessary that the memory included in the main control system storeinformation related to a plurality of feet which are planned to bereplaced. Accordingly, the number of memories or the capacity of thememory can be reduced. Alternatively, the memory can be used for storingother information.

In addition, only the foot sole, instead of the entire body of the foot,is replaced in the above-described construction, and the instep can beefficiently used in common for all kinds of foot soles. Since the shapeand material of a portion which comes into contact with the road surface(foot bottom) generally have large influence on the adaptation of thefoot to various states of road surfaces, it is sufficient if thisportion is replaced.

The information related to the main foot body or the foot sole includesinformation necessary for the control system of the robot's main bodywhich controls the overall motion of the robot to perform trajectorycalculation of the foot or the foot sole and other processes necessaryfor motion control. The information related to the main foot body or thefoot sole is not particularly limited, and it may include, for example,identification information, shape (shape of the ground-contact surfacewhich comes into contact with the road surface, etc.), material, weight,and coefficient of friction of the foot bottom surface of the main footbody or the foot sole, and the number, arrangement, and characteristics(both static and dynamic) of sensors (force sensors for detecting theZMP, an acceleration sensor for detecting collision or inclination ofthe road surface, a ground-contact detection sensor, etc.) mounted onthe main foot body or the foot sole. It is not necessary that all of theabove-mentioned information elements be included in the informationrelated to the main foot body or the foot sole as long as one of them isincluded.

The memory means may be an electronic memory device such as a ROM, anEPROM, and a SRAM. In addition, the memory means may also be a memorydevice using an arrangement such as a barcode and pins, a memory deviceusing symbols and characters, a memory device in which information isrecorded magnetically or optically, a mechanical switch, and othervarious memory devices. In such cases, read-out means suitable for thememory means (for example, a processing device such as a CPU, an imagingdevice such as a CCD, etc.) is used, and the read-out means may eitherbe of a contact-type or a non-contact type.

In addition to the main control system of the robot's main body, afoot-mounted control system which communicates with the main controlsystem may be provided on the main foot body or the instep. In thiscase, the information is read out from the memory means by thefoot-mounted control system, and is transmitted directly, or after beingsubjected to a certain process, to the main control system of therobot's main body.

In addition, according to another aspect of the present invention, alegged mobile robot includes a movable leg, an instep attached to an endportion of the movable leg, and a foot sole attached to the instep suchthat the foot sole can move along a plane approximately parallel to afoot bottom surface. The “foot bottom surface” refers to a surfaceincluding a portion of the foot sole which comes into contact with afloor surface when the legged mobile robot is in an upright position ona flat floor surface (if there are a plurality of such portions, asurface including all of them).

Since the foot sole can move along a plane approximately parallel to thefoot bottom surface, even when there are bumps and depressions on theroad surface and a part of the foot sole interferes with them when theidling leg is placed on the road surface, the foot sole can move alongthe above-described surface so as to eliminate such interference orabsorb the force applied by the road surface. Accordingly, the stablemotion of the robot can be continued.

The foot sole may include a bottom portion which faces the bottomsurface of the instep and side portions which face side surfaces of theinstep with gaps therebetween, so that the foot sole can move within arange corresponding to the gaps between the side surfaces of the instepand the side portions. When the legged mobile robot walks, there is arisk that not only the bottom surface of the foot but also the sidesurfaces thereof will strike or interfere with an object. However, whenthe above-described construction is used, the side portions of themovable foot sole strike or interfere with the object and the entirebody of the foot sole moves along the bottom surface of the instep.Accordingly, the motion can be continued without degrading thestability.

In addition, buffer means may be disposed between the foot sole and theinstep. The buffer means may be constructed of elastic means, viscousmeans, or the combination of the elastic means and the viscous means.When the buffer means is provided, the impact transmitted from the footsole to the instep can be reduced, and vibration of the foot sole can besuppressed. Accordingly, noise can be reduced. In addition, in the casein which the foot sole can simply move along the bottom surface of theinstep, sufficient effect thereof may not be obtained when the foot soleis at the end of the movable range. However, when the buffer means isprovided, the foot sole can be placed at a suitable position relative tothe instep when no external force is applied to the foot sole.

In addition, when the buffer means including both the elastic means andthe viscous means is provided, the elasticity coefficient of the elasticmember and the viscosity coefficient of the viscous member arepreferably set such that the vibration of the foot sole which occurswhen the foot sole leaves the road surface in the walking motion of themovable leg is reduced to a predetermined amount before the foot sole isplaced on the road surface again. When vibration greater than thepredetermined extent remains when the idling leg is placed on the roadsurface, there is a risk that the trajectory calculation and othercalculations necessary for control which are performed by the controlsystem of the robot must be corrected. The predetermined extent refersto a minimum necessary vibration which can be tolerated while thecontrol system of the robot achieves stable walking motion.

In addition, according to another aspect of the present invention, alegged mobile robot includes a movable leg, control means forcontrolling the motion of the movable leg, and a foot provided on an endportion of the movable leg. The foot includes a main foot body attachedto the movable leg, at least one sensor provided on the main foot bodyfor detecting information used for controlling the motion of the movableleg, and foot-mounted processing means provided on the main foot bodyfor performing a predetermined calculation process on the basis of anoutput from the sensor in accordance with the kind of the sensor.

Alternatively, a legged mobile robot includes a main foot body attachedto the movable leg, at least one sensor provided on the main foot bodyfor detecting information used for controlling the motion of the movableleg, foot-mounted processing means provided on the main foot body forperforming a predetermined calculation process on the basis of an outputfrom the sensor in accordance with the kind of the sensor, andcommunication means for supplying an output from the foot-mountedprocessing means to the control means.

Alternatively, a foot of a legged mobile robot which is provided on anend portion of a movable leg includes an instep attached to the movableleg, a foot sole which is movably attached to the instep, at least onesensor provided on the instep for detecting information used forcontrolling the motion of the movable leg, and foot-mounted processingmeans provided on the instep for performing a predetermined calculationprocess on the basis of an output from the sensor in accordance with thekind of the sensor.

Alternatively, a legged mobile robot includes an instep attached to themovable leg, a foot sole which is movably attached to the instep, atleast one sensor provided on the instep for detecting information usedfor controlling the motion of the movable leg, foot-mounted processingmeans provided on the instep for performing a predetermined calculationprocess on the basis of an output from the sensor in accordance with thekind of the sensor, and communication means for supplying an output fromthe foot-mounted processing means to the control means.

The sensor may be, for example, a force sensor or an accelerationsensor. However, the kind and the purpose of installation of the sensorare not particularly limited. The foot-mounted processing means performsa calculation process corresponding to the kind, the purpose ofinstallation, etc., of the sensor. For example, the foot-mountedprocessing means may calculate the ZMP of the foot on the basis ofoutputs from force sensors provided at a plurality of (at least three)positions for detecting pressures applied vertically to a surface (footbottom surface) including a ground-contact portion on the bottom surfaceof the main foot body or the foot sole which comes into contact with theground. In addition, the foot-mounted processing means may also performcalculations for detecting collision of the foot with an obstacle orstumbling motion based on an outputs from an acceleration sensor orcalculations for determining the inclination angle of the road surfaceon which the foot is placed based on an output from an accelerationsensor.

According to the present invention, since the foot-mounted processingmeans which calculates the ZMP is provided on the main foot body or theinstep and the foot-mounted processing means calculates the ZMP on thebasis of the outputs from the sensors, the control means of the robot'smain body can simply receive the calculation results and control themotion of the movable leg on the basis of information including thecalculation results. Accordingly, it is not necessary for the controlmeans of the robot's main body to perform the ZMP calculation, and thecontrol means of the robot's main body can be dedicated to othercalculation processes for, for example, motion control of the movableleg. Thus, the processing load on the control means can be reduced. As aresult, processes with high urgency can be performed without delay, andcomplex motions which require a large amount of calculation can beachieved.

In addition, when the sensors are optimized in accordance with therelationship with the foot-mounted processing means, the foot-mountedprocessing means can be adapted to various sensors of different kinds,characteristics, numbers, etc. In other words, the foot can bemodularized. Accordingly, changes required in the mechanism of therobot's main body and information stored therein due to the replacementof the foot can be reduced, and the task of replacing the foot can befacilitated.

In addition, since the sensors are provided on the instep along with thefoot-mounted processing means for calculating the ZMP on the basis ofthe outputs from the sensors, different from the case in which thesensors are provided on the foot sole, wires for connecting the sensorsto the foot-mounted processing means do not include moving portions.Therefore, the movement of the foot sole can be prevented from beingimpeded by the wires and the wires can be prevented from being damagedby the movement of the foot sole. In particular, when the ZMP-detectionsensors are provided on the bottom surface of the instep, theZMP-detection sensors receive pressures from the top surface of the footsole, which is equivalent to the road surface in view of ZMP detection,and errors in detection values due to the variation in the state of theroad surface can be reduced. Accordingly, the ZMP can be detected moreaccurately.

The main foot body may be detachably attached to the movable leg withattaching/detaching means.

Alternatively, the foot sole may be detachably attached to the instepwith attaching/detaching means. In addition, attaching/detaching meansfor detachably attaching the instep to the movable leg may also be usedin addition to or instead of the attaching/detaching means fordetachably attaching the foot sole to the instep.

According to the present invention, since the foot-mounted processingmeans for processing the outputs from the sensors provided on the mainfoot body or the instep is provided on the main foot body or the instep,the control means of the robot's main body can simply receive theprocessing results and control the motion of the movable leg on thebasis of information including the processing results. Accordingly, itis not necessary for the control means of the robot's main body toperform the processes based on the outputs from the sensors provided onthe main foot body or the instep (for example, ZMP calculation isperformed if the ZMP-detection sensors are provided and processes forcalculating the inclination of the road surface or detecting thestumbling motion are performed if the acceleration sensor is provided),and the control means of the robot's main body can be dedicated to othercalculation processes for, for example, motion control of the movableleg. Thus, the processing load on the control means can be reduced. As aresult, processes with high urgency can be performed without delay, andcomplex motions which require a large amount of calculation can beachieved.

In addition, in the known structure, an exclusive wire must be providedfor each sensor in order to supply the detection values of the sensorsprovided on the main foot body or the instep to the control means.However, since the detection values are first processed by thefoot-mounted processing means and the processing results are transmittedto the control means, wiring can be made simpler.

In addition, when the sensors provided on the main foot body or theinstep are optimized in accordance with the relationship with thefoot-mounted processing means, the foot-mounted processing means can beadapted to various sensors of different kinds, characteristics, numbers,etc. In other words, the foot can be modularized. Accordingly, changesrequired in the mechanism of the robot's main body and informationstored therein due to the replacement of the foot can be reduced, andthe task of replacing the foot can be facilitated.

In addition, since the sensors are provided on the instep along with thefoot-mounted processing means for processing the outputs from thesensors, wires for connecting the sensors to the foot-mounted processingmeans do not include movable portions. Therefore, the movement of thefoot sole can be prevented from being impeded by the wires and the wirescan be prevented from being damaged by the movement of the foot sole.

In addition, in the case in which the foot sole is attached to theinstep such that the foot sole can move along a plane approximatelyparallel to the foot bottom surface, even when there are bumps anddepressions on the road surface and a part of the foot sole interfereswith them, the foot sole can move along the above-described surface soas to eliminate such interference or absorb the force applied by theroad surface. Accordingly, the stable motion of the robot can becontinued.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a “human-shaped” legged mobile robot 100according to a first embodiment of the present invention which is in anupright position.

FIG. 2 is a rear view of the legged mobile robot 100 in an uprightposition.

FIG. 3 is a diagram showing a schematic construction of a control systemof the legged mobile robot 100.

FIG. 4 is a perspective view of a foot of the legged mobile robot shownin FIG. 1 according to a first example.

FIG. 5 is a side view of the foot of the legged mobile robot shown inFIG. 1 according to the first example.

FIG. 6 is a bottom view of the foot of the legged mobile robot shown inFIG. 1 according to the first example.

FIG. 7 is a sectional view of FIG. 6 cut along line A-A.

FIG. 8 is a sectional view of FIG. 6 cut along line B-B.

FIG. 9 is a perspective view of a foot of the legged mobile robotaccording to a second example.

FIG. 10 is a sectional side view of the foot of the legged mobile robotaccording to the second example.

FIG. 11 is a perspective view of a foot of the legged mobile robotaccording to a third example.

FIG. 12 is a side view of the foot of the legged mobile robot accordingto the third example.

FIG. 13 is a bottom view of the foot of the legged mobile robotaccording to the third example.

FIG. 14 is a diagram for explaining dimensions of the foot of the leggedmobile robot shown in FIG. 11.

FIG. 15 is a diagram for explaining the shape of a doorsill which isassumed to be stepped on by the foot of the legged mobile robot shown inFIG. 11.

FIG. 16 is a perspective view of a foot of the legged mobile robotaccording to a fourth example.

FIG. 17 is a side view of the foot of the legged mobile robot accordingto the fourth example.

FIG. 18 is a bottom view of the foot of the legged mobile robotaccording to the fourth example.

FIG. 19 is a sectional view of FIG. 18 cut along line A-A.

FIG. 20 is a sectional view of FIG. 18 cut along line B-B.

FIG. 21 is a sectional view of FIG. 18 cut along line C-C.

FIG. 22 is a diagram for explaining dimensions of the foot of the leggedmobile robot shown in FIG. 16.

FIG. 23 is a diagram for explaining the shape of a doorsill which isassumed to be stepped on by the foot of the legged mobile robot shown inFIG. 16.

FIG. 24 is a perspective view of a foot of the legged mobile robotaccording to a fifth example.

FIG. 25 is a side view of the foot of the legged mobile robot accordingto the fifth example.

FIG. 26 is a bottom view of the foot of the legged mobile robotaccording to the fifth example.

FIG. 27 is a sectional view of FIG. 26 cut along line A-A.

FIG. 28 is a sectional view of FIG. 26 cut along line B-B.

FIG. 29 is a sectional view of FIG. 26 cut along line C-C .

FIG. 30 is a perspective view of a foot of the legged mobile robotaccording to a sixth example.

FIG. 31 is a side view of the foot of the legged mobile robot accordingto the sixth example.

FIG. 32 is a bottom view of the foot of the legged mobile robotaccording to the sixth example.

FIG. 33 is a diagram for explaining dimensions of the foot of the leggedmobile robot shown in FIG. 30.

FIG. 34 is a diagram for explaining the shape of a doorsill which isassumed to be stepped on by the foot of the legged mobile robot shown inFIG. 30.

FIG. 35 is a perspective view of a foot of the legged mobile robotaccording to a seventh example.

FIG. 36 is a side view of the foot of the legged mobile robot accordingto the seventh example.

FIG. 37 is a bottom view of the foot of the legged mobile robotaccording to the seventh example.

FIG. 38 is a sectional view of FIG. 37 cut along line A-A.

FIG. 39 is a sectional view of FIG. 37 cut along line B-B.

FIG. 40 is a perspective view of a foot of the legged mobile robotaccording to an eighth example.

FIG. 41 is a side view of the foot of the legged mobile robot accordingto the eighth example.

FIG. 42 is a side view of a foot of the legged mobile robot according toa ninth example.

FIG. 43 is a bottom view of the foot of the legged mobile robotaccording to the ninth example.

FIG. 44 is a bottom view of a foot of the legged mobile robot accordingto a tenth example.

FIG. 45 is a side view of the foot of the legged mobile robot accordingto the tenth example.

FIG. 46 is a plan view showing a foot of the legged mobile robotaccording to an eleventh structure.

FIG. 47 is a diagram for explaining a behavior of the foot of the leggedmobile robot according to the eleventh structure when the robot fallsover.

FIG. 48 is a plan view showing a foot of the legged mobile robotaccording to a twelfth structure.

FIG. 49 is a diagram for explaining a behavior of the foot of the leggedmobile robot according to the twelfth structure when the robot fallsover.

FIG. 50 is a plan view showing a foot of the legged mobile robotaccording to a thirteenth structure.

FIG. 51 is a plan view showing a foot of the legged mobile robotaccording to a fourteenth structure.

FIG. 52 is a diagram showing the state in which the foot of the leggedmobile robot deforms due to the weight.

FIG. 53 is a diagram showing the state in which the foot of the leggedmobile robot is placed on a step.

FIG. 54 is a diagram showing the state in which the foot of the leggedmobile robot walks on a carpet.

FIG. 55 is a diagram for explaining the motion of the foot of the leggedmobile robot when the corners of the bottom surface of the foot arerounded.

FIG. 56 is a diagram showing the state in which a concavity stepped onby the foot of the legged mobile robot reaches the bottom surface(ceiling surface) of a plantar-arch portion through a flexible portionof the foot.

FIG. 57 is a diagram showing the state in which the foot of the leggedmobile robot steps on a relatively large step.

FIG. 58 is a diagram showing the manner in which the flexible portion ofthe foot of the legged mobile robot deforms when the flexible portion isformed of a normal elastic material.

FIG. 59 is a diagram showing the manner in which the flexible portion ofthe foot of the legged mobile robot deforms when the flexible portion isformed of a material with a relatively high flexibility.

FIG. 60 is a diagram showing the state in which the foot of the leggedmobile robot steps on an obstacle which can roll.

FIG. 61 is a diagram showing the state in which the foot of the leggedmobile robot steps on a relatively large obstacle which can roll.

FIG. 62 is a diagram showing the state in which the foot of the leggedmobile robot moves on a carpet.

FIG. 63 is a side view showing a support structure of an instep (upperportion of a foot) and a foot bottom (sole of the foot) according to afirst example.

FIG. 64 is a sectional view of FIG. 63 cut along lint A-A.

FIG. 65 is a perspective view showing a support structure of an instep(upper portion of a foot) and a foot bottom (sole of the foot) accordingto a second example.

FIG. 66 is a sectional view of FIG. 65 cut along lint B-B.

FIG. 67 is a plan view showing a support structure of an instep (upperportion of a foot) and a foot bottom (sole of the foot) according to athird example.

FIG. 68 is a partially broken side view showing a support structure ofan instep (upper portion of a foot) and a foot bottom (sole of the foot)according to a third example.

FIG. 69 is a sectional view showing a connection/replacement structureof a leg and a foot at an ankle according to a first example.

FIG. 70 is a sectional view showing the construction of the foot shownin FIG. 69 and a connecting part in the state in which the foot isconnected to the ankle.

FIG. 71 is a diagram showing a connection/replacement structure of a legand a foot at an ankle according to a second example, where (A) is a topview, (B) is a side view, (C) is a back view, and (D) is a sectionalside view when the foot is removed from the ankle.

FIG. 72 is a diagram showing a state in which the structure of the footaccording to the second example is changed, where (A) is a top view, (B)is a side view, (C) is a back view, and (D) is a sectional side viewwhen the foot is connected to the ankle.

FIG. 73 is a sectional view showing the construction of a foot and aconnecting part according to a third example in the state in which thefoot is connected to an ankle.

FIG. 74 is a block diagram showing the structure of an instep circuitunit and a foot-sole circuit unit included in the foot.

FIG. 75 is an exploded side view showing a part of aconnection/replacement structure of a leg and a foot according to afourth example.

FIG. 76 is a plan view of the foot included in theconnection/replacement structure of the leg and the foot according tothe fourth example.

FIG. 77 is an exploded side view showing a part of the foot included inthe connection/replacement structure of the leg and the foot accordingto the fourth example.

FIG. 78 is a bottom view of the foot included in theconnection/replacement structure of the leg and the foot according tothe fourth example.

FIG. 79 is a diagram showing a connection/replacement structure of a legand a foot according to a fifth example, and is a sectional view showingthe construction of the foot and a connecting part in the state in whichthe foot is removed from an ankle.

FIG. 80 is a diagram showing the connection/replacement structure of theleg and the foot according to the fifth example, and is a sectional viewshowing the construction of the foot and the connecting part in thestate in which the foot is connected to the ankle.

FIG. 81 is a bottom view of an instep included in theconnection/replacement structure of the leg and the foot according tothe fifth example.

FIG. 82 is a diagram showing the state in which a known foot of a leggedmobile robot deforms due to the weight.

FIG. 83 is a diagram for,explaining a resistive-force-generationeffective surface in the case in which the foot is in point contact witha road surface.

FIG. 84 is a diagram for explaining the resistive-force-generationeffective surface in the case in which the foot is in contact with theroad surface such that the contact area is frame-shaped.

FIG. 85 is a diagram showing the state in which the known foot of thelegged mobile robot is placed on a step.

FIG. 86 is a diagram showing the state in which the known foot of thelegged mobile robot walks on a carpet.

FIG. 87 is a diagram for explaining the motion of the known foot of thelegged mobile robot when a corner of the bottom surface of the foot iscaught by the road surface.

FIG. 88 is a diagram showing the state in which the known foot of thelegged mobile robot is placed a step.

FIG. 89 is a diagram showing the state in which a known foot of thelegged mobile robot having a plantar arch is placed on a step.

FIG. 90 is a plan view showing an example of the construction of a foot.

FIG. 91 is a plan view showing another example of the construction of afoot.

FIG. 92 is a plan view showing another example of the construction of afoot.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings.

Overall Construction

First, the overall construction of a legged mobile robot will bedescribed below with reference to FIGS. 1 to 3.

FIG. 1 is a front view of a “human-shaped” legged mobile robot 100according to a first embodiment of the present invention which is in anupright position. In addition, FIG. 2 is a rear view of the leggedmobile robot 100 in an upright position.

As shown in the figures, the legged mobile robot 100 includes left andright lower limbs 110 used as movable legs for performing leggedlocomotion, a trunk 120, left and right upper limbs 130, and a head 140.

Each of the left and right lower limbs 110 includes a thigh 111, a kneejoint 112, a shank 113, an ankle 114, and a foot 150, and is connectedto the trunk 120 at the bottom end of the trunk 120 by a hip joint 115.

In addition, each of the left and right upper limbs 130 includes anupper arm 131, an elbow joint 132, and a forearm 133. The left and rightupper limbs 130 are connected to the trunk 120 at the upper left end andthe upper right end, respectively, of the trunk 120 by shoulder joints134.

In addition, the head 140 is connected to the trunk 120 at the center ofthe top end of the trunk 120 by a neck joint 141.

For convenience, in the following descriptions regarding the foot 150, aplane including a portion of the bottom surface of the foot 150 whichcomes into contact with a road surface (floor surface) is defined as anX-Y plane. In addition, an axis which extends in the front-reardirection of the robot is defined as an X axis, an axis which extends inthe right-left direction of the robot is defined as a Y axis, and anaxis which is perpendicular to the X and Y axes is defined as a Z axis.

In addition, in the drawings, reference character R denotes smoothlycurved portions.

Each of the joints is provided with actuators, and motions of the robotare achieved by driving the actuators. In order to satisfy variousrequirements such as a requirement for reducing excessive swellings tomake the robot's appearance similar to the natural form of human beingsand a requirement for performing attitude control of the unstablestructure to achieve biped walking motion thereof, small, lightactuators are preferably used. Accordingly, the legged mobile robot 100of the present embodiment includes small AC servo actuators which can bedirectly connected to gears and in which a single-chip servo controlleris installed in a motor unit. An example of a small AC servo actuator isdisclosed in Japanese Patent Application No. 11-3386 which is applied bythe present applicant.

Although not shown in FIGS. 1 and 2, a main control unit and peripheraldevices such as a power supply circuit are contained in the trunk 120.

Control System

Next, a control system of the above-described legged mobile robot 100will be described below with reference to FIG. 3.

FIG. 3 shows the construction of a control system of the legged mobilerobot 100. A main control unit (control means) 300 includes a centralprocessing unit (CPU) 301, a random access memory (RAM) 302, a read onlymemory (ROM) 303 which stores motion patterns, etc., an A/D converter305 which converts analog signals output from various sensors 306mounted in the legged mobile robot 100 to digital signals, and a bus 304which provides connection between them.

A ROM 305 provided on the foot 150 is also connected by the bus 304.This will be described in more detail below.

The CPU 301 determines the motion of the legged mobile robot 100 on thebasis of information stored in the ROM 303 and outputs from the sensors306, and generates control signals including motion commands which areto be transmitted to AC servo actuators 307 provided on each joint.Then, the CPU 301 supplies the control signals for each joint to the ACservo actuators 307 connected to the main control unit 300 via the bus304. Accordingly, the AC servo actuators 307 are activated on the basisof the motion commands included in the control signals, and the leggedmobile robot 100 performs various motions such as walking motion.

The main control unit and peripheral devices such as the power supplycircuit of the legged mobile robot 100 are disposed in an inner space ofthe trunk 120 of the legged mobile robot 100, which is not shown inFIGS. 1 and 2.

Foot

A first example 150 a of the foot 150 will be described below withreference to FIGS. 4 to 8.

FIG. 4 is a perspective view of the first example 150 a of the foot;FIG. 5 is a side view thereof; FIG. 6 is a bottom view thereof; FIG. 7is a sectional view of FIG. 6 cut along line A-A; and FIG. 8 is asectional view of FIG. 6 cut along line B-B.

The foot 150 a according to a first structure includes a main foot body160 constructed of a rectangular plate-shaped member and a connector 161which is formed integrally with the main foot body 160 on a top surface162 of the main foot body and which is connected to the ankle 114 of thecorresponding lower limb 110.

The bottom surface (foot bottom surface) of the main foot body 160includes a slope 172 which extends from a peripheral portion of thebottom surface and gently slopes toward the center of the main foot bodyso as to form a dome-shaped first concavity (recess) 170.

In addition, a flexible portion 190 is formed on the surface of thefirst concavity 170. When an external force is applied to the flexibleportion 190, the flexible portion 190 deforms while exerting apredetermined elastic force as a reaction force, and when the externalforce is removed, the flexible portion 190 returns to its originalshape.

The flexible portion 190 is formed by supplying a predetermined flexiblematerial into the first concavity 170 such that the flexible materialcovers the surface of the first concavity 170 and the inner space of thefirst concavity 170 is partially filled with the flexible material andsuch that the surface of the flexible portion 190 does not come intocontact with the road surface when the foot 150 a is placed thereon ifthe road surface is flat.

The flexible material may be any material that has elasticity,viscosity, or flexibility, such as rubber, clay, and urethane. Morespecifically, a material having hysteresis characteristics, for example,a material which requires a relatively long time to return to itsoriginal shape or a material having shape-memory property, such asα-gel, memory foam, a component obtained by enclosing powders in a bag,etc., is preferably used as the flexible material.

In the foot 150 a having the above-described construction, theperipheral portion which surrounds the first concavity 170 and whichprojects most in the bottom surface of the main foot body 160 serves asa ground-contact portion 165 which actually comes into contact with theground-contact surface (walking surface). Accordingly, when the footbottom surface (ground-contact surface) of the main foot body 160 isplaced on the road surface, the ground-contact portion 165 comes intoeven contact with the road surface and supports the weight of the leggedmobile robot 100, while the surfaces of the first concavity 170 and theflexible portion 190 disposed in the first concavity 170 are separatedfrom the road surface.

In addition, the edges at the periphery of the bottom surface of themain foot body 160, that is, portions between side surfaces 163 of themain foot body 160 and the ground-contact portion 165 or between theside surfaces 163 and the slope 172 of the first concavity are formed assmooth curved surfaces (R surfaces) 164. Accordingly, stumbling of thelegged mobile robot 100 caused when, for example, one of the edges atthe periphery of the foot 150 a strikes a bump on the road surface or ispushed into the road surface can be prevented. In addition, even whenthe legged mobile robot 100 is in a danger of falling over, the motionof the legged mobile robot 100 can be smoothly changed to safe fallingmotion.

The foot 150 a according to the first example has the above-describedconstruction. Since the foot 150 a includes the first concavity 170 inthe bottom surface of the main foot body 160 at an area inside theground-contact portion 165, even when the position of the ZMP varies anddeformation of the foot 150 a occurs as the legged mobile robot walks,variation in the position and the shape of the ground-contact portion165 is extremely small. Accordingly, variation in the shape of theabove-described resistive-force-generation effective surface andreduction in the area thereof can be reduced. As a result, variation inthe resistive force against the moment about the yaw axis can bereduced, and unexpected change in the behavior of the robot does noteasily occur. In addition, the possibility that spinning motion in whichthe robot rotates around the ground-contact portion will occur can bereduced. Accordingly, the attitude stability of the robot can beincreased and the stable motion of the robot can be continued.

In addition, since the first concavity is separated from the roadsurface, a contact pressure applied to the road surface can be increasedand the robustness against the moment about the yaw axis generated inthe legged mobile robot can be increased accordingly. In addition, theexcessive increase in the frictional force between the foot and the roadsurface can be prevented, which also helps to prevent the stumbling ofthe robot.

In addition, in the foot 150 a, the flexible portion 190 is disposed inthe concavity 170 formed in the bottom surface of the foot 150 a.Accordingly, even in a situation which cannot be dealt with by otherportions of the foot 150 a, for example, even when there is a risk ofdangerous behavior, such as sliding, suitable countermeasures can beimplemented. The state and the movement of the foot 150 a in such aspecial situation will be described in detail below.

The main foot body 160 is preferably composed of a light, strongmaterial such as an aluminum alloy and a magnesium alloy.

A second example 150 b of the foot 150 will be described below withreference to FIGS. 9 and 10. FIG. 9 is a perspective view of the secondexample 150 b of the foot, and FIG. 10 is a sectional view thereof.

The foot 150 b includes a main foot body 200 constructed of arectangular plate-shaped member and a connector 201 which is formedintegrally with the main foot body 200 on a top surface 202 of the mainfoot body and which is connected to the ankle 114 of the correspondinglower limb 110. The bottom surface (foot bottom surface) of the mainfoot body 200 includes a slope 212 which extends from a peripheralportion of the bottom surface and gently slopes inward so as to form adome-shaped first concavity (recess) 210.

In addition, notches are formed in the peripheral portion of the bottomsurface of the foot 150 b at the central positions of the inner andouter sides of the peripheral portion, the notches being cut along thesurface (ceiling surface) of the first concavity 210 so that the mainfoot body 200 does not come into contact with the floor surface (walkingsurface) at those positions. More specifically, notches are formed inthe peripheral portion of the main foot body 200, which serves assidewalls of the first concavity 210, such that a tunnel-shaped openingwhich extends in the lateral direction (direction perpendicular to thewalking direction) is provided at the central position of the main footbody 200. The overall concavity formed in the bottom surface of the mainfoot body 200 including the first concavity 210 and the notches 206 atthe left and right sides serves as a plantar-arch portion 207 of thefoot 150 b.

Similar to the foot 150 a according to the first example, a flexibleportion 230 is formed on the surface of the first concavity 210. When anexternal force is applied to the flexible portion 230, the flexibleportion 230 deforms while exerting a predetermined elastic force as areaction force, and when the external force is removed, the flexibleportion 230 returns to its original shape.

The flexible portion 230 is formed by supplying a predetermined flexiblematerial into the first concavity 210 such that the flexible materialcovers the surface of the first concavity 210 and the inner space of thefirst concavity 210 is partially filled with the flexible material andsuch that the surface of the flexible portion 230 does not come intocontact with the road surface when the foot 150 b is placed thereon ifthe road surface is flat. The material of the flexible portion 230 maybe the same as that of the above-described first foot 150 a, andexplanations thereof are thus omitted.

In the foot 150 b having the above-described construction, bottomportions which surround the first concavity 210 and which project mostin the bottom surface of the main foot body 200, that is, bottomportions in front of and behind the plantar-arch portion 207, serve asground-contact portions 205 which actually come into contact with theground-contact surface (walking surface). Accordingly, when the footbottom surface (ground-contact surface) of the main foot body 200 isplaced on the road surface, the ground-contact portions 205 come intoeven contact with the road surface and support the weight of the leggedmobile robot 100, while the surfaces of the plantar-arch portion 207 andthe flexible portion 230 are separated from the road surface.

In addition, the edges at the periphery of the bottom surface of themain foot body 200, that is, portions between side surfaces 203 of themain foot body 200 and the ground-contact portions 205 or between theside surfaces 203 and the slope 212 of the first concavity are formed assmooth curved surfaces (R surfaces) 204. Accordingly, stumbling of thelegged mobile robot 100 caused when, for example, one of the edges atthe periphery of the foot 150 a strikes a bump on the road surface or ispushed into the road surface can be prevented. In addition, even whenthe legged mobile robot 100 is in a danger of falling over, the motionof the legged mobile robot 100 can be smoothly changed to safe fallingmotion.

Similar to the foot 150 a of the first example, since the foot 150 b ofthe second example includes the plantar-arch portion 207 in the bottomsurface of the main foot body 200, even when the position of the ZMPvaries and deformation of the foot 150 b occurs as the legged mobilerobot walks, variation in the shape of the resistive-force-generationeffective surface and reduction in the area thereof can be reduced. As aresult, variation in the resistive force against the moment about theyaw axis can be reduced, and unexpected change in the behavior of therobot does not easily occur. In addition, the possibility that spinningmotion in which the robot rotates around the ground-contact portion willoccur can be reduced. Accordingly, the attitude stability of the robotcan be increased and the stable motion of the robot can be continued.

In addition, since the plantar-arch portion is separated from the roadsurface, a contact pressure applied to the road surface can be increasedand the robustness against the moment about the yaw axis generated inthe legged mobile robot can be increased accordingly. In addition, theexcessive increase in the frictional force between the foot and the roadsurface can be suppressed, which helps to prevent the stumbling of therobot. In addition, in the foot 150 b, the flexible portion 230 isdisposed in the concavity 210 formed in the bottom surface of the foot150 b. Accordingly, even in a situation which cannot be dealt with byother portions of the foot 150 b, for example, even when there is a riskof dangerous behavior, such as sliding, suitable countermeasures can beimplemented. The state and the movement of the foot 150 b in such aspecial situation will be described in detail below.

The main foot body 200 is preferably composed of a light, strongmaterial such as an aluminum alloy and a magnesium alloy.

A third example 150 c of the foot 150 will be described below withreference to FIGS. 11 to 15.

FIG. 11 is a perspective view of the third example 150 c of the foot,FIG. 12 is a side view thereof, and FIG. 13 is a bottom view thereof. Inaddition, FIGS. 14 and 15 are diagrams for explaining suitabledimensions of the foot 150 c.

The foot 150 c includes a main foot body 240 constructed of arectangular plate-shaped member and a connector 241 which is formedintegrally with the main foot body 240 on a top surface 242 of the mainfoot body and which is connected to the ankle 114 of the correspondinglower limb 110.

The bottom surface (foot bottom surface) of the main foot body 240includes slopes 252 which extend from a peripheral portion of the bottomsurface and gently slope inward so as to form a dome-shaped firstconcavity (recess) 250. In addition, a columnar second concavity(recess) 260 is formed deeper into the main foot body 240 than the firstconcavity 250 at the central area of the main foot body 240.

In addition, notches are formed in the peripheral portion of the bottomsurface of the foot 150 c at the central positions of the inner andouter sides of the peripheral portion, the notches being cut to thebottom surface (ceiling surface) of the second concavity 260 so that themain foot body 240 does not come into contact with the floor surface(walking surface) at those positions. In other words, the bottom surface(ceiling surface) of the first concavity 250 and sidewalls of the secondconcavity 260 are partially removed at the central positions of thebottom surface of the main foot body 240 in the X direction, so that thesecond concavity extends through the main foot body 240 in the lateraldirection (Y direction) thereof at the central position in the walkingdirection. The overall concavity formed in the bottom surface of themain foot body 240 including the first concavity 250, the secondconcavity 260, and the notches 246 serves as a plantar-arch portion 247of the foot 150 c.

A flexible portion 270 is formed on the surface of the second concavity260. When an external force is applied to the flexible portion 270, theflexible portion 270 deforms while exerting a predetermined elasticforce as a reaction force, and when the external force is removed, theflexible portion 270 returns to its original shape. The flexible portion270 is formed by supplying a predetermined flexible material into thesecond concavity 260 such that the flexible material covers the bottomsurface (ceiling surface) 261 of the second concavity 260 and the innerspace of the second concavity 260 is partially filled with the flexiblematerial and such that the surface of the flexible portion 270 does notcome into contact with the road surface when the foot 150 c is placedthereon if the road surface is flat. The material of the flexibleportion 270 may be the same as that of the above-described first foot150 a, and explanations thereof are thus omitted.

In the foot 150 c having the above-described construction, peripheralportions of the first concavity 250 which project most in the bottomsurface of the main foot body 240 serve as ground-contact portions 245which actually come into contact with the ground-contact surface(walking surface). Accordingly, when the foot bottom surface(ground-contact surface) of the main foot body 240 is placed on the roadsurface, the ground-contact portions 245 come into even contact with theroad surface and support the weight of the legged mobile robot 100,while the plantar-arch portion 247 is separated from the road surface.

In addition, side surfaces 262 of the second concavity 260 arediscontinuously connected to the slopes 252 of the first concavity 250such that edges are provided therebetween, and are formed such that theyare approximately parallel to the vertical direction (Z direction) whichis perpendicular to the ground-contact surface. Since the side surfacesof the second concavity 260 are constructed as described above, when,for example, the robot walks on a soft floor, such as a carpet, and softobjects such as fibers of the carpet enter the second concavity 260, thesoft objects encounter the side surfaces of the second concavity 260 andare caught by the discontinuous edges. As a result, resistive force andreaction force are applied to the fibers against the moving direction ofthe fibers, and frictional force is applied to the walking surface ofthe foot 150 c. Accordingly, even on a slippery walking surface asdescribed above, sufficient frictional force can be obtained, andefficiencies of braking force and impelling force can be increased.

In addition, end portions 253, which are parts of the slopes of thefirst concavity 250 and the side surfaces of the second concavity 260and which face the notches 246, are formed of smooth curved surfaces (Rsurfaces), as shown in FIG. 13. Accordingly, the amount of indentationin a soft moving surface, such as a carpet, can be adjusted andgeneration of the falling moment can be prevented. In addition, thefloor surface can be protected.

In addition, the edges at the periphery of the bottom surface of themain foot body 240, that is, portions between side surfaces 243 of themain foot body 240 and the ground-contact portions 245 are formed assmooth curved surfaces (R surfaces) 244. Accordingly, stumbling of thelegged mobile robot 100 caused when, for example, one of the edges atthe periphery of the foot 150 c strikes a bump on the road surface or ispushed into the road surface can be prevented. In addition, even whenthe legged mobile robot 100 is in a danger of falling over, the motionof the legged mobile robot 100 can be smoothly changed to safe fallingmotion.

Next, dimensions of the foot 150 c of the third example will bedescribed below with reference to FIGS. 14 and 15. The size of the foot150 c may be arbitrarily determined in accordance with, for example, theoverall size of the legged mobile robot. However, in the case in whichthe legged mobile robot walks in a Japanese house, it can be assumedthat a doorsill of a “fusuma” (Japanese sliding door) having grooves andbumps would be a major barrier to the walking motion of the small leggedmobile robot. Therefore, it is extremely effective to limit thedimensions of the foot 150 c under predetermined conditions for thepurpose of making the robot walk stably on the doorsill. The conditionsunder which the legged mobile robot can walk stably even when the foot150 c steps on the doorsill will be described below.

In this case, the sizes of the ground-contact portions 245 of the foot150 c must be set such that the ground-contact portions 245 do not fallinto the grooves of the doorsill. As shown in FIG. 14, in the foot 150c, end portions in front of and behind the first concavity 250 serve asthe ground-contact portions 245. In addition, the peripheral edges ofthe ground-contact portions 245 are connected to the side surfaces 243of the main foot body 240 with the smooth curved surfaces 244, and edgesof the ground-contact portions 245 which are closer to the center of themain foot body are connected to the gently slopes 252 of the firstconcavity 250. Thus, it can be assumed that the areas from the slopes252 to the curved surfaces at the peripheral edges of the main foot body240 are the ground-contact areas which project from main foot body andwhich should be prevented from falling into the grooves of the doorsill.Accordingly, with reference to FIG. 14, conditions are set on thelengths L₁ and L₂ of the contact areas in the walking direction (Xdirection), the overall length L of the foot 150 c, and the width W ofthe foot 150 c, that is, the length of the contact areas in the lateraldirection (Y direction).

Doorsills used in Japanese houses are shaped as shown in, for example,FIG. 15. FIG. 15(A) shows a doorsill with two grooves, and FIG. 15(B)shows a doorsill with three grooves. In FIGS. 15(A) and 15(B), widths ofthe grooves are L_(g1), L_(g2), and L_(g3), and those of bumps areL_(m1) and L₂. In common doorsills, L_(g1)=L_(g2)=L_(g3)=21 mm andL_(m1)=L_(m2)=12 mm are satisfied.

When the legged mobile robot walks in a normal walking direction, inorder to prevent the foot 150 c from falling into the grooves of thedoorsill with two grooves, the dimensions of the contact areas and thefoot must satisfy the following expression:L ₁ , L ₂ >L _(g1)(=L _(g2))L>L _(g1) +L _(m1) +L _(g2)   (1)

In addition, when the legged mobile robot walks in the normal walkingdirection, in order to prevent the foot 150 c from falling into thegrooves of the doorsill with three grooves, the dimensions of thecontact areas and the foot must satisfy the following expression:L ₁ , L ₂ >L _(g1)(=L _(g2))L>L _(g1) +L _(m1) +L _(g2)L ₁ , L ₂ <L _(m1) +L _(g1) +L _(m2)   (2)

Accordingly, when the above-described common doorsills are considered,L₁, L₂>21 mm and L>54 mm must be satisfied to prevent the foot 150 c ofthe legged mobile robot from falling into the grooves of the doorsillwith two grooves, and 21<L₁, L₂<45 mm and L>54 mm must be satisfied toprevent the foot 150 c of the legged mobile robot from falling into thegrooves of the doorsill with three grooves. In the foot 150 c of thepresent example, L=105.8 mm, W=69.8 mm, and L1=L2=33 mm are satisfied.

When the legged mobile robot walks sideways, it is also necessary to seta condition on the length of the foot 150 c in the lateral directionsimilarly to the case in which it walks in the normal walking direction.However, this will not be discussed here since the foot 150 c is notdivided in the lateral direction and has a sufficient length relative tothe widths of the grooves of the doorsill.

The foot 150 c has the above-described construction, and similar to thefeet 150 a and 150 b of the first and second examples, since the foot150 c includes the plantar-arch portion 247 in the bottom surface of themain foot body 200, even when the position of the ZMP varies anddeformation of the foot 150 c occurs as the legged mobile robot walks,variation in the shape of the resistive-force-generation effectivesurface and the reduction in the area thereof can be reduced. As aresult, variation in the resistive force against the moment about theyaw axis can be reduced, and unexpected change in the behavior of therobot does not easily occur. In addition, the possibility that so-calledspinning motion in which the robot rotates around the ground-contactportion will occur can be reduced. Accordingly, the attitude stabilityof the robot can be increased and the stable motion of the robot can becontinued.

In addition, since the plantar-arch portion is separated from the roadsurface, a contact pressure applied to the road surface can be increasedand the robustness against the moment about the yaw axis generated inthe legged mobile robot can be increased accordingly. In addition, theexcessive increase in the frictional force between the foot and the roadsurface can be suppressed, which also helps to prevent the stumbling ofthe robot.

In addition, in the foot 150 c, the flexible portion 270 is disposed inthe second concavity 260 formed in the bottom surface of the foot 150 c.Accordingly, even in a situation which cannot be dealt with by otherportions of the foot 150 c, for example, even when there is a risk ofdangerous behavior, such as slipping, suitable countermeasures can beimplemented. The state and the movement of the foot 150 c in such aspecial situation will be described in detail below.

The main foot body 160 is preferably composed of a light, strongmaterial such as an aluminum alloy and a magnesium alloy.

A fourth example of the foot 150 will be described below with referenceto FIGS. 16 to 23.

FIG. 16 is a perspective view of the foot 150; FIG. 17 is a side view ofthe foot 150; FIG. 18 is a bottom view of the foot 150; FIG. 19 is asectional view of FIG. 18 cut along line A-A; FIG. 20 is a sectionalview of FIG. 18 cut along line B-B; and FIG. 21 is a sectional view ofFIG. 18 cut along line C-C. In addition, FIGS. 22 and 23 are diagramsfor explaining suitable dimensions of the foot 150.

The foot 150 includes a main foot body 240 constructed of a rectangularplate-shaped member and a connector 241 which is formed integrally withthe main foot body 240 on a top surface 242 of the main foot body andwhich is connected to the ankle 114 of the corresponding lower limb 110.

The bottom surface (foot bottom surface) of the main foot body 240includes slopes 252 which extend from four corners of the bottom surfaceand gently slope inward so as to form a first concavity (recess) 250 ofan imaginarily dome-like shape. In addition, a second concavity (recess)260 of an imaginary columnar shape is formed deeper into the main footbody 240 than the first concavity 250 at the central area of the mainfoot body 240.

In addition, grooves 246 a to 246 d are formed in a peripheral portionof the bottom surface of the foot 150 at the central positions of foursides of the peripheral portion, the grooves 246 a to 246 d having thesame depth as the that of the bottom surface (ceiling surface) of thesecond concavity 260 and extending from the central area of the mainfoot body 240 to the outside of the main foot body so that the main footbody 240 does not come into contact with the floor surface (walkingsurface) at those positions.

Accordingly, the concavity formed in the bottom surface of the main footbody 240 including the first concavity 250, the second concavity 260,and the grooves 246 serves as a plantar-arch portion 247 of the foot150. The plantar-arch portion 247 generally refers to the concavityformed in the bottom surface of the foot 150. More specifically, any oneof the concavities forming the four grooves 246 a to 246 d, continuousgrooves which extend in the lateral direction and the walking direction,and the overall concavity formed in the foot 150 may be referred to asthe plantar-arch portion.

Since the bottom surface of the foot 150 is divided by the four grooves246 a to 246 d, four projections are provided on the bottom surface ofthe foot 150 at the four corners thereof. In each of the projections, aportion which projects most serves as a ground-contact portion 245 whichactually comes into contact with the ground-contact surface (walkingsurface).

Although the above-described projections include the slopes 252 of thefirst concavity 250 and smooth curved surfaces 244 formed at the cornersof the second concavity 260, which will be described below, portions atwhich the boundary areas between the slopes 252 and the curved surfaces244 project most serve as the ground-contact portions 245.

When the foot bottom surface (ground-contact surface) of the main footbody 240 is placed on the road surface, the ground-contact portions 245come into even contact with the road surface and support the weight ofthe legged mobile robot 100, while the plantar-arch portion 247 isseparated from the road surface.

A flexible portion 270 is formed on the surface of the second concavity260. When an external force is applied to the flexible portion 270, theflexible portion 270 deforms while exerting a predetermined elasticforce as a reaction force, and when the external force is removed, theflexible portion 270 returns to its original shape.

The flexible portion 270 is formed by supplying a predetermined flexiblematerial into the second concavity 260 such that the flexible materialcovers the bottom surface (ceiling surface) 261 of the second concavity260 and the inner space of the second concavity 260 is partially filledwith the flexible material and such that the surface of the flexibleportion 270 does not come into contact with the road surface when thefoot 150 is placed thereon if the road surface is flat.

The flexible material may be any material that has elasticity,viscosity, or flexibility, such as rubber, clay, and urethane. Morespecifically, a material having hysteresis characteristics, for example,a material which requires a relatively long time to return to itsoriginal shape or a material having shape-memory property, such asα-gel, memory foam, a component obtained by enclosing powders in a bag,etc., is preferably used as the flexible material.

In addition, side surfaces 262 of the second concavity 260 and thegrooves 246 are discontinuously connected to the slopes 252 of the firstconcavity 250 such that edges are provided therebetween, and are formedsuch that they are approximately parallel to the vertical direction (Zdirection) which is perpendicular to the ground-contact surface. Sincethe side surfaces 262 of the second concavity 260 and the notches 246are constructed as described above, when, for example, the robot walkson a soft floor, such as a carpet, and soft objects such as fibers ofthe carpet enter the plantar-arch portion 247, the soft objectsencounter the side surfaces 262 and are caught by the discontinuousedges. As a result, resistive force and reaction force are applied tothe fibers against the moving direction of the fibers, and frictionalforce is applied to the walking surface of the foot 150. Accordingly,even on a slippery walking surface as described above, sufficientfrictional force can be obtained, and efficiencies of braking force andimpelling force can be increased.

In addition, end portions 253 of the side surfaces 262 of the notches246 which are near the openings in the side surfaces of the main footbody 240 are formed of smooth curved surfaces (R surfaces), as shown inFIG. 6. Accordingly, the amount of indentation in a soft moving surface,such as a carpet, can be adjusted and generation of the falling momentcan be prevented. In addition, the floor surface can be protected.

In addition, the edges at the periphery of the bottom surface of themain foot body 240, that is, portions between side surfaces 243 of themain foot body 240 and the ground-contact portions 245 or between theside surfaces 243 and the slopes 252 of the first concavity 250 areformed as smooth curved surfaces (R surfaces) 244. Accordingly,stumbling of the legged mobile robot 100 caused when, for example, oneof the edges at the periphery of the foot 150 strikes a bump on the roadsurface or is pushed into the road surface can be prevented. Inaddition, even when the legged mobile robot 100 is in a danger offalling over, the motion of the legged mobile robot 100 can be smoothlychanged to safe falling motion. The main foot body 160 is preferablycomposed of a light, strong material such as an aluminum alloy and amagnesium alloy.

Next, dimensions of the foot 150 will be described below with referenceto FIGS. 22 and 23.

The size of the foot 150 may be arbitrarily determined in accordancewith, for example, the overall size of the legged mobile robot. However,in the case in which the legged mobile robot walks in a Japanese house,it can be assumed that a doorsill of a “fusuma” (Japanese sliding door)having grooves and bumps would be a major barrier to the walking motionof the small legged mobile robot. Therefore, it is extremely effectiveto limit the dimensions of the foot 150 under predetermined conditionsfor the purpose of making the robot walk stably on the doorsill. Theconditions under which the legged mobile robot can walk stably even whenthe foot 150 steps on the doorsill will be described below.

In this case, the sizes of the ground-contact portions 245 of the foot150 must be set such that the ground-contact portions 245 do not fallinto the grooves of the doorsill. As shown in FIG. 10, in the foot 150,end portions in front of and behind the first concavity 250 serve as theground-contact portions 245. In addition, the peripheral edges of theground-contact portions 245 are connected to the side surfaces 243 ofthe main foot body 240 with the smooth curved surfaces 244, and edges ofthe ground-contact portions 245 which are closer to the center of themain foot body are connected to the gently slopes 252 of the firstconcavity 250. Thus, it can be assumed that the projecting areas fromthe slopes 252 to the curved surfaces at the peripheral edges of themain foot body 240 are the ground-contact areas which project from mainfoot body and which should be prevented from falling into the grooves ofthe doorsill.

If the legged mobile robot walks only in the normal walking direction,it is only necessary to restrict the dimensions of the foot 150 in thedirection perpendicular to the grooves of the doorsill, that is, thewalking direction (X direction). However, in this example, a case inwhich the legged mobile robot walks sideways and steps on the doorsillis also considered. Accordingly, the dimensions of the foot 150 in thelateral direction (Y direction) which is perpendicular to the walkingdirection are also considered under the same conditions of the doorsill.

Accordingly, in the foot 150 of the present example, with reference toFIG. 22, conditions are set on the lengths L₁ and L₂ of the contactareas in the walking direction (X direction), the overall length L ofthe overall foot 150, the lengths W₁ and W₂ of the contact areas in thelateral direction (Y direction), and the overall width W of the foot150.

Doorsills used in Japanese houses are shaped as shown in, for example,FIG. 11. FIG. 23(A) shows a doorsill with two grooves, and FIG. 23(B)shows a doorsill with three grooves. In FIGS. 23(A) and 23(B), widths ofthe grooves are L_(g1), L_(g2), and L_(g3), and those of bumps areL_(m1), and L_(m2). In common doorsills, L_(g1)=L_(g2)=L_(g3)=21 mm andL_(m1)=L_(m2)=12 mm are satisfied.

When the legged mobile robot walks in a normal walking direction, inorder to prevent the foot 150 from falling into the grooves of thedoorsill with two grooves, the dimensions of the contact areas and thefoot must satisfy the following expression:L ₁ , L ₂ >L _(g1)(=L _(g2))L>L _(g1) +L _(m1) +L _(g2)   (3)

In addition, when the legged mobile robot walks in the normal walkingdirection, in order to prevent the foot 150 from falling into thegrooves of the doorsill with three grooves, the dimensions of thecontact areas and the foot must satisfy the following expression:L ₁ , L ₂ >L _(g1)(=L _(g2))L>L _(g1) +L _(m1) +L _(g2)L ₁ , L ₂ <L _(m1) +L _(g1) +L _(m2)   (4)

Accordingly, L₁, L₂>21 mm and L>54 mm must be satisfied to prevent thefoot 150 of the legged mobile robot from falling into the grooves of thedoorsill with two grooves, and 21<L₁, L₂<45 mm and L>54 mm must besatisfied to prevent the foot 150 of the legged mobile robot fromfalling into the grooves of the doorsill with three grooves.

In addition, when the legged mobile robot walks in the lateraldirection, in order to prevent the foot 150 from falling into thegrooves of the doorsill with two grooves, the dimensions of the contactareas and the foot must satisfy the following expression:W ₁ , W ₂ >L _(g1)(=L _(g2))W>L _(g1) +L _(m1) +L _(g2)   (3)

In addition, when the legged mobile robot walks in the lateraldirection, in order to prevent the foot 150 from falling into thegrooves of the doorsill with three grooves, the dimensions of thecontact areas and the foot must satisfy the following expression:W ₁ , W ₂ >L _(g1)(=L _(g2))W>L _(g1) +L _(m1) +L _(g2)W ₁ , W ₂ <L _(m1) +L _(g2) +L _(m2)   (6)

Accordingly, W₁, W₂>21 mm and W>54 mm must be satisfied to prevent thefoot 150 of the legged mobile robot from falling into the grooves of thedoorsill with two grooves, and 21<W₁, W₂<45 mm and W>54 mm must besatisfied to prevent the foot 150 of the legged mobile robot fromfalling into the grooves of the doorsill with three grooves.

The actual size of the foot 150 is L=105.8 mm, W=69.8 mm, and L1=L2=33mm, and all of the above-described conditions are satisfied.

A fifth example of the foot 150 will be described below with referenceto FIGS. 24 to 29.

FIGS. 24 to 29 show a perspective view, a side view, a bottom view, andsectional views of a foot 150 b.

As shown in the figures, in the foot 150 b, a ceiling surface of asecond concavity is dome-shaped, and a flexible portion 190 isconstructed in a different manner. The structure of the foot may bearbitrarily determined such that a desired behavior can be achieved inaccordance with the walking environment, obstacles, etc.

For example, the flexible portions 190 and 230 are formed so as to coverthe inner surfaces of the first concavities 170 and 210, respectively.In addition, in the foot 150, the flexible portion 270 is formed so asto cover the ceiling surface 261 of the second concavity 260. However,in any of the above-described cases, it is not necessary that theflexible portion cover the entire region of the corresponding surface.The flexible portion may also be formed such that it covers only a partof the first concavity or the second concavity, or be selectively formedat an area where a possibility that bumps on the road surface will enteris high. In addition, a plurality of flexible portions may also beprovided. Accordingly, the construction of the flexible portion may bedetermined arbitrarily.

In addition, although an elastic and viscous material having hysteresischaracteristics is preferably used as the material of the flexibleportion in the above-described examples, the material of the flexibleportion is not limited to this as long as it has flexibility. Forexample, a material which does not have hysteresis characteristics mayalso be used for applications where hysteresis characteristics are notnecessary.

In addition, although the side surfaces 262 of the second concavity 260extend along the direction approximately perpendicular to theground-contact surface, that is, the vertical direction, in the foot150, the present invention is not limited to this. More specifically,the side surfaces 262 of the second concavity 260 may be inclined at anyangle as long as the inclination thereof is closer to vertical than theslopes 252 of the first concavity 250.

The above examples of feet of the legged mobile robot are described inorder to facilitate understanding of the present invention, and are notintended to limit the scope of the present invention. The componentsdescribed in the above-described examples may be replaced with othercomponents of different design or equivalents which belong to thetechnical scope of the present invention. In addition, variousmodifications are possible.

For example, in the feet 150 a and 150 b according to the first andsecond examples, respectively, the flexible portions 190 and 230 areformed so as to cover the inner surfaces of the first concavities 170and 210, respectively. In addition, in the foot 150 c of the thirdexample, the flexible portion 270 is formed so as to cover the ceilingsurface 261 of the second concavity 260. However, in any of theabove-described cases, it is not necessary that the flexible portioncover the entire region of the corresponding surface. The flexibleportion may also be formed such that it covers only a part of the firstconcavity or the second concavity, or be selectively formed at an areawhere a possibility that bumps on the road surface will enter is high.In addition, a plurality of flexible portions may also be provided.Accordingly, the construction of the flexible portion may be determinedarbitrarily.

In addition, although it is described above that an elastic and viscousmaterial having hysteresis characteristics is preferably used as thematerial of the flexible portion, the material of the flexible portionis not limited to this as long as it has flexibility. For example, amaterial which does not have hysteresis characteristics may also be usedfor applications where hysteresis characteristics are not necessary.

In addition, although the side surfaces 262 of the second concavity 260extend along the direction approximately perpendicular to theground-contact surface, that is, the vertical direction, in the foot 150c, the present invention is not limited to this. More specifically, theside surfaces 262 of the second concavity 260 may be inclined at anyangle as long as the inclination thereof is closer to vertical than theslopes 252 of the first concavity 250.

In addition, in the foot 150 c, the slopes 252 of the first concavity250 and the side surfaces 262 of the second concavity 260 arediscontinuously connected to each other such that, for example, edges ofa predetermined angle are provided therebetween. However, they may alsobe connected with smooth curved surfaces similarly to the edges of thebottom surface of the main foot body 240. The shapes, etc., of the sidesurfaces 262 of the second concavity 260 and the edges thereof may bearbitrarily determined in accordance with conditions and environments,for example, whether or not the robot is planned to walk on a softsurface, characteristics of the soft surface, etc.

In addition, the shape of the concavity formed in the bottom surface ofthe foot 150 is not limited to the dome shape (cone shape), and theconcavity may have an arbitrary shape as long as it has a slope (forexample, a tapered surface) which extend continuously from theground-contact portions 265 toward the inside of the main foot body 240.For example, the concavity may have a quadrangular pyramidal shape, acircular conical shape, an arch shape, a tunnel shape, etc.

A sixth example of the foot 150 will be described below with referenceto FIGS. 30 to 34.

FIGS. 30 to 32 are diagrams showing the construction of the foot 150,where FIG. 30 is a perspective view, FIG. 31 is a side view, and FIG. 32is a bottom view of the foot 150.

The foot 150 includes a main foot body 160 constructed of a rectangularplate-shaped member and a connector 161 which is formed integrally withthe main foot body 160 on a top surface 162 of the main foot body andwhich is connected to the ankle 114 of the corresponding lower limb 110.

The bottom surface (foot bottom surface) of the main foot body 160includes slopes 172 which extend from a peripheral portion of the bottomsurface and gently slope inward so as to form a dome-shaped firstconcavity (recess) 170. In addition, a columnar second concavity(recess) 180 is formed deeper into the main foot body 160 than the firstconcavity 170 at the central region of the main foot body 160.

In addition, notches are formed in the peripheral portion of the bottomsurface of the foot 150 at the central positions of the inner and outersides of the peripheral portion, the notches being cut to the bottomsurface (ceiling surface) of the second concavity 180 so that the mainfoot body 160 does not come into contact with the floor surface (walkingsurface) at those positions. In other words, the bottom surface (ceilingsurface) of the first concavity 170 and sidewalls of the secondconcavity 180 are partially removed at the central positions of thebottom surface of the main foot body 160 in the X direction, so that thesecond concavity extends through the main foot body 160 in the lateraldirection (Y direction) thereof at the central region in the walkingdirection. The overall concavity formed in the bottom surface of themain foot body 160 including the first concavity 170, the secondconcavity 180, and the notches 165 serves as a plantar-arch portion 166of the foot 150.

In the foot 150, peripheral portions of the first concavity 170 whichproject most in the bottom surface of the main foot body 160 serve asground-contact portions 171 which actually come into contact with theground-contact surface (walking surface). Accordingly, when the footbottom surface (ground-contact surface) of the main foot body 160 isplaced on the road surface, the ground-contact portions 171 come intoeven contact with the road surface and support the weight of the leggedmobile robot 100, while the plantar-arch portion 166 is separated fromthe road surface.

In addition, side surfaces of the second concavity 180 arediscontinuously connected to the slopes 172 of the first concavity 170such that edges are provided therebetween, and are formed such that theyare approximately parallel to the vertical direction (Z direction) whichis perpendicular to the ground-contact surface. Since the side surfacesof the second concavity 180 are constructed as described above, when,for example, the robot walks on a soft floor, such as a carpet, and softobjects such as fibers of the carpet enter the second concavity 180, thesoft objects encounter the side surfaces of the second concavity 180 andare caught by the discontinuous edges. As a result, resistive force andreaction force are applied to the fibers against the moving direction ofthe fibers, and frictional force is applied to the walking surface ofthe foot 150. Accordingly, even on a slippery walking surface asdescribed above, sufficient frictional force can be obtained, andefficiencies of braking force and impelling force can be increased.

In addition, end portions 173, which are parts of the slopes of thefirst concavity 170 and the side surface of the second concavity 180 andwhich face the notches 165, are formed of smooth curved surfaces (Rsurfaces). Accordingly, the amount of indentation in a soft movingsurface, such as a carpet, can be adjusted and generation of the fallingmoment can be prevented. In addition, the floor surface can beprotected.

In addition, the edges at the periphery of the bottom surface of themain foot body 160, that is, portions between side surfaces 163 of themain foot body 160 and the ground-contact portions 171 are formed assmooth curved surfaces (R surfaces) 164. Accordingly, stumbling of thelegged mobile robot 100 caused when, for example, one of the edges atthe periphery of the foot 150 strikes a bump on the road surface or ispushed into the road surface can be prevented. In addition, even whenthe legged mobile robot 100 is in a danger of falling over, the motionof the legged mobile robot 100 can be smoothly changed to safe fallingmotion.

The main foot body 160 is preferably composed of a light, strongmaterial such as an aluminum alloy and a magnesium alloy.

Next, dimensions of the foot 150 will be described below with referenceto FIGS. 33 and 34. The size of the foot 150 may be arbitrarilydetermined in accordance with, for example, the overall size of thelegged mobile robot. However, in the case in which the legged mobilerobot walks in a Japanese house, it can be assumed that a doorsill of a“fusuma” (Japanese sliding door) having grooves and bumps would be amajor barrier to the walking motion of the small legged mobile robot. Itis extremely effective to limit the dimensions of the foot 150 underpredetermined conditions for the purpose of making the robot walk stablyon the doorsill. The conditions under which the legged mobile robot canwalk stably even when the foot 150 steps on the doorsill will bedescribed below.

In this case, the size of the ground-contact portions 171 of the foot150 must be set such that the ground-contact portions 171 do not fallinto grooves of the doorsill. As shown in FIG. 33, in the foot 150, endportions in front of and behind the first concavity 170 serve as theground-contact portions 171. In addition, the peripheral edges of theground-contact portions 171 are connected to the side surfaces 163 ofthe main foot body 160 with the smooth curved surfaces 164, and edges ofthe ground-contact portions 171 which are closer to the center of themain foot body are connected to the gently slopes 172 of the firstconcavity 170. Thus, it can be assumed that the areas from the slopes172 to the curved surfaces at the peripheral edges of the main foot body160 are the ground-contact areas which project from main foot body andwhich should be prevented from falling into the grooves of the doorsill.

Accordingly, with reference to FIG. 33, conditions are set on thelengths L₁ and L₂ of the contact areas in the walking direction (Xdirection), the overall length L of the foot 150 c, and the width W ofthe foot 150 c, that is, the length of the contact areas in the lateraldirection (Y direction).

Doorsills used in Japanese houses are shaped as shown in, for example,FIG. 34. FIG. 34(A) shows a doorsill with two grooves, and FIG. 34(B)shows a doorsill with three grooves. In FIGS. 34(A) and 34(B), widths ofthe grooves are L_(g1), L_(g2), and L_(g3), and those of bumps areL_(m1) and L_(m2). In common doorsills, L_(g1)=L_(g2)=L_(g3)=21 mm andL_(m1)=L_(m2)=12 mm are satisfied.

When the legged mobile robot walks in a normal walking direction, inorder to prevent the foot 150 from falling into the grooves of thedoorsill with two grooves, the dimensions of the contact areas and thefoot must satisfy the following expression:L ₁ , L ₂ >L _(g1)(=L _(g2))L>L _(g1) +L _(m1) +L _(g2)   (7)

In addition, when the legged mobile robot walks in the normal walkingdirection, in order to prevent the foot 150 c from falling into thegrooves of the doorsill with three grooves, the dimensions of thecontact areas and the foot must satisfy the following expression:L ₁ , L ₂ >L _(g1)(=L _(g2))L>L _(g1) +L _(m1) +L _(g2)L ₁ , L ₂ <L _(m1) +L _(g1) +L _(m2)   (8)

Accordingly, L₁, L₂>21 mm and L>54 mm must be satisfied to prevent thefoot 150 c of the legged mobile robot from falling into the grooves ofthe doorsill with two grooves, and 21<L₁, L₂<45 mm and L>54 mm must besatisfied to prevent the foot 150 c of the legged mobile robot fromfalling into the grooves of the doorsill with three grooves. In the foot150 c, L=105.8 mm, W=69.8 mm, and L1=L2=33 mm are satisfied.

When the legged mobile robot walks sideways, it is also necessary to seta condition in the lateral direction of the foot 150 similarly to thecase in which it walks in the normal walking direction. However, thiswill not be discussed here since the ground-contact area of the foot 150is not divided in the lateral direction by, for example, a plantar-arcportion and the foot 150 has a sufficient length relative to the widthsof the grooves of the doorsill.

A seventh example of the foot 150 will be described below with referenceto FIGS. 35 to 39. FIG. 35 is a perspective view; FIG. 36 is a sideview; FIG. 37 is a bottom view; FIG. 38 is a sectional view of FIG. 37cut along line A-A; and FIG. 39 is a sectional view of FIG. 37 cut alongline B-B.

The foot according to a seventh structure includes a main foot body 1000which is constructed of a rectangular plate-shaped member and which isconnected to the ankle 114 of the corresponding lower limb 110. The mainfoot body 1000 is preferably composed of a light, strong material suchas an aluminum alloy and a magnesium alloy.

A connector 1002 for providing connection to the ankle 114 is formedintegrally with the main foot body 1000 on a top surface 1001 of themain foot body 1000. In addition, a ground-contact portion 1003 isformed on the bottom surface (foot bottom surface) of the main foot body1000 at the peripheral region thereof (see the hatched area in FIG. 6).A plantar-arch portion 1004 having a slope 1005 which slopes inward soas to form a concavity is formed in the bottom surface of the main footbody 1000 at an area inside the ground-contact portion 1003.

The plantar-arch portion 1004 is dome-shaped and is connected to theground-contact portion 1003 at the periphery thereof. Accordingly, whenthe foot bottom surface of the main foot body 1000 is placed on the roadsurface, the ground-contact portion 1003 comes into even contact withthe road surface, while the plantar-arch portion 1004 is separated fromthe road surface. The shape of the plantar-arch portion 1004 is notlimited to the dome shape, and may also be a quadrangular pyramidalshape or a circular conical shape (cone shape). In addition, theplantar-arch portion 1004 may also have other shapes as long as it has aslope (for example, a tapered surface) which extends continuously fromthe ground-contact portion 1002 and which slopes inward.

Side surfaces 1006 of the main foot body 1000 and the ground-contactportion (ground-contact surface) 1003 are connected to each other withsmooth curved surfaces (R surfaces) 1007. Preferably, the ground-contactportion 1003 and the plantar-arch portion 1004 are also connected toeach other with smooth curved surfaces.

Since the main foot body 1000 includes the plantar-arch portion 1004 inthe foot bottom surface of the main foot body 1000 at an area inside theground-contact portion 1003, even when the position of the ZMP variesand deflection of the main foot body 1000 occurs as the legged mobilerobot walks, variation in the position and the shape of theground-contact portion 1003 is extremely small. Accordingly, variationin the resistive force against the moment about the yaw axis can bereduced, and unexpected change in the behavior of the robot does noteasily occur. In addition, the possibility that the spinning motion(motion in which the robot rotates around the ground-contact portion)will occur can be reduced. Accordingly, the attitude stability of therobot can be increased and the stable motion of the robot can becontinued. In addition, since the plantar-arch portion 1004 is separatedfrom the road surface, the ground-contact portion 1003 is separated fromthe center of the main foot body 1000. Accordingly, the area of theground-contact portion 1003 is reduced without reducing the resistiveforce against moment around the yaw axis. Therefore, the excessiveincrease in the frictional force between the foot and the road surfacecan be prevented, which also helps to prevent the stumbling of therobot.

In addition, since the side surfaces 1006 of the main foot body 1000 andthe ground-contact portion 1003 are connected to each other with thesmooth R surfaces 1007, these portions can be prevented from beingcaught by a road surface having bumps and depressions and stumbling ofthe robot can be prevented. Accordingly, the possibility that the robotwill fall over can be reduced.

In addition, since the plantar-arch portion 1004 is provided, even whenthere are bumps and depressions on the road surface and the central areaof the foot bottom surface is positioned above a bump on the roadsurface, the possibility that the foot will step on the bump and fallinto a so-called seesaw state can be reduced.

An eighth example of the foot 150 will be described below with referenceto FIGS. 40 and 41. FIG. 40 is a perspective view and FIG. 41 is asectional side view.

The foot according to an eighth structure includes a main foot body 1100which is constructed of a rectangular plate-shaped member and which isconnected to the ankle 114 of the corresponding lower limb 110. The mainfoot body 1100 is preferably composed of a light, strong material suchas an aluminum alloy and a magnesium alloy.

A connector 1101 for providing connection to the ankle 114 is formedintegrally with the main foot body 1100 on the top surface of the mainfoot body 1100. In addition, ground-contact portions 1102 are formed onthe bottom surface (foot bottom surface) of the main foot body 1100 atthe front and rear ends thereof. A plantar-arch portion 1103 is formedin the bottom surface of the main foot body 1100 at an area inside theground-contact portions 1102.

The plantar-arch portion 1103 is dome-shaped and is connected to theground-contact portions 1102 at the front and rear ends thereof. Inaddition, the plantar-arch portion 1103 is directly connected to theside surfaces of the main foot body 1100 at the left and right sidesthereof. Accordingly, when the foot bottom surface of the main foot body1100 is placed on the road surface, the ground-contact portions 1102comes into even contact with the road surface, while the plantar-archportion 1103 extend through the main foot body 1100 in the lateraldirection. The shape of the plantar-arch portion 1103 is not limited tothe dome shape, and may also be a quadrangular pyramidal shape or acircular conical shape (cone shape). In addition, the plantar-archportion 1103 may also have other shapes as long as it has a slope (forexample, tapered surfaces) which extends continuously from theground-contact portions 1102 and which slopes inward.

Side surfaces 1104 of the main foot body 1100 and the ground-contactportions (contact surfaces) 1102 are connected to each other with smoothcurved surfaces (R surfaces). Preferably, the ground-contact portions1102 and the plantar-arch portion 1103 are also connected to each otherwith smooth surfaces.

A ninth example of the foot 150 will be described below with referenceto FIGS. 42 and 43. FIG. 42 is a sectional side view and FIG. 43 is abottom view.

The foot according to a ninth structure includes a main foot body 1200which is constructed of a rectangular plate-shaped member and which isconnected to the ankle 114 of the corresponding lower limb 110. The mainfoot body 1200 is preferably composed of a light, strong material suchas an aluminum alloy and a magnesium alloy.

A connector 1201 for providing connection to the ankle 114 is formedintegrally with the main foot body 1200 on the top surface of the mainfoot body 1200. In addition, four ground-contact portions 1202 a to 1202d are formed in the bottom surface (foot bottom surface) of the mainfoot body 1200 at the corners thereof. A plantar-arch portion 1205 isformed in the bottom surface of the main foot body 1200 at an areasurrounded by the ground-contact portions 1202 a to 1202 d. Theplantar-arch portion 1205 has a pair of slopes 1203 and a circular flatportion 1204 which is approximately parallel to a plane including theground-contact portions 1202 a to 1202 d. The flat portion 1204 isprovided for ensuring the strength of the main foot body 1200 since themain foot body 1200 is relatively thin. If the main foot body 1200 issufficiently thick, the flat portion 1204 may be omitted and the slopesmay be formed such that the depth increases toward the center of themain foot body 1200.

The slopes 1203 are formed such that they slope inward, and the averageinclination thereof may be, for example, {fraction (1/20)}. The slopes1203 may be flat surfaces, circular conical surfaces, or surfaces ofother shapes. In this case, the slopes 1203 are circular conicalsurfaces (cone-shaped surfaces) in which the inclination angle increasestoward the center and decreases toward the left and right ends.

The detailed dimensions of each part will be described below forreference. The thickness of the main foot body 1200 at the areas wherethe ground-contact portions 1202 a to 1202 d are formed is t1=5 mm; thethickness of the main foot body 1200 at the area where the flat portion1204 is formed is t2=4.2 mm; the radius of the curved surfaces betweenthe ground-contact portions and the side surfaces is r1=4 mm; the radiusof the curved surfaces between the side surfaces is r2=4 mm; thediameter of the flat portion is d=66 mm; the length of the diagonallines between the ground-contact portions 1202 a and 1202 d or betweenthe ground-contact portions 1202 b to 1202 c is D=100 mm; the dimensionof each slope 1203 at the central position is m1=12 mm; and thedimension of each slope 1203 at both sides is m2=30 mm.

The construction may also be such that the ground-contact portions 1202a and 1202 b are linearly connected to each other (at the constantheight) and the ground-contact portions 1202 c and 1202 d are linearlyconnected to each other (at the constant height) so that linearground-contact portions are provided. Alternatively, the areas betweenthe ground-contact portions 1202 a and 1202 b and between theground-contact portions 1202 c and 1202 d may be dented inward in an arcshape or other shape. In such a case, the slopes 1203 are formed suchthat they are smoothly connected to the shapes of these areas.

A tenth example of the foot 150 will be described below with referenceto FIGS. 44 and 45. FIG. 44 is a plan view and FIG. 45 is a partiallysectioned side view.

The foot according to a tenth structure includes an instep 1310 which isconnected to the ankle 114 of the corresponding lower limb 110 and afoot sole 1320 which directly comes into contact with the road surface,and has a two-part structure in which the foot sole 1320 is movablyattached to the instep 1310.

The instep 1310 is constructed of a rectangular plate-shaped member anda connector 1311 for providing connection to the ankle 114 is formedintegrally with the instep 1310 on the top surface of the instep 1310.Although not shown in the figure, a plurality of force sensors fordetecting pressures in the Z-axis direction which are used forcalculating the ZMP are provided on the bottom surface of the instep1310. In the present example, four force sensors are disposed at fourcorners of the bottom surface of the instep 1310.

Each of these force sensors includes a metal diaphragm and four straingauges, and is constructed by forming a bridge circuit with the fourstrain gauges and laminating the stain gauges on the metal diaphragm.However, the force sensors are not limited to this, and those havingother constructions may also be used.

The foot sole 1320 is a rectangular box-shaped member with an open topwhich includes a bottom plate 1321 and upright side plates 1322 whichare formed integrally with the bottom plate 1321 along the peripheralsides of the bottom plate 1321. The top surface of the bottom plate 1321is in contact with the bottom surface of the instep 1310. In addition,the bottom surface of the bottom plate 1321 serves as the foot bottomsurface of the foot 150. The bottom surface of the bottom plate 1321 andouter surfaces of the side plates 1322 are connected to each other withR surfaces (arc surfaces) or smooth curved surfaces.

The foot sole 1320 is provided with ground-contact portions 1323 at fourcorners thereof. In addition, a plantar-arch portion 1326 is formed inthe bottom surface of the foot sole 1320 at an area surrounded by theground-contact portions 1323. The plantar-arch portion 1323 has a pairof slopes 1324 and a circular flat portion 1325 which is approximatelyparallel to a plane including the ground-contact portions.

The slopes 1324 are formed such that they slope inward, and may be flatsurfaces, circular conical surfaces, or surfaces of other shapes.

The internal shape of the side plates 1322 of the foot sole 1320 issimilar to the shape of side surfaces of the instep 1310, but isslightly larger. The side surfaces of the instep 1310 face the innersurfaces of the side plates 1322 of the foot sole 1320 with small gaps(allowances) therebetween. Accordingly, the foot sole 1320 can moverelative to the instep 1310 along the bottom surface of the instep 1310,that is, in an arbitrary direction in the X-Y plane.

The foot sole 1320 is attached to the instep 1310 with a retainingmechanism (not shown) in such a manner that the foot sole 1320 does notfall from the instep 1310 when the corresponding leg is off the roadsurface and the movement of the foot sole 1320 in the X-Y plane is notrestricted. The retaining mechanism preferably has a mechanism foreasily attaching/detaching the foot sole 1320 when the foot sole 1320 isto be replaced.

A buffer (buffer means) 1330 is disposed between the side plates 1322 ofthe foot sole 1320 and the side surfaces of the instep 1310. In thisexample, an endless rubber sheet is used as the buffer 1330, and isdisposed such that gaps between the inner surfaces of the side plates1322 of the foot sole 1320 and the side surfaces of the instep 1310 arecompletely filled with the rubber sheet. However, the buffer is notlimited to this, and a leaf spring, a sponge, a solid or semi-solidviscous means may also be used.

The buffer is preferably formed such that the gaps between the innersurfaces of the side plates 1322 of the foot sole 1320 and the sidesurfaces of the instep 1310 are completely filled since foreign mattercan be prevented from entering the gaps in such a case. However, thepresent invention is not limited to this, and a plurality of buffers maybe arranged with gaps therebetween. In addition, the buffer may also beomitted.

An eleventh example of the foot 150 will be described below withreference to FIGS. 46 and 47. FIG. 46 is a plan view showing theschematic construction of the foot according to an eleventh structure.Although FIG. 46 shows only one of the feet attached to the left andright legs, the construction of the other one of the feet isplane-symmetric to that of the foot shown in the figure.

The foot according to the eleventh structure includes a main foot body1110 which is constructed of a rectangular plate-shaped member and whichis connected to the ankle 114 of the corresponding lower limb 110. Themain foot body 1110 is preferably composed of a light, strong materialsuch as an aluminum alloy and a magnesium alloy.

A connector 1111 for providing connection to the ankle 114 is formedintegrally with the main foot body 1110 on the top surface of the mainfoot body 1110. In addition, the bottom surface (foot bottom surface) ofthe main foot body 1110 serves as the ground-contact surface. In theexample shown in the figure, the foot bottom surface is flat.

As shown in the figure, the external shape of the foot bottom surface isrectangular. Although not particularly limited, a plurality of non-slipgrooves or a plantar-arch portion having a concave shape may be formedin the foot bottom surface. Although not shown in the figure, the shapeof the plantar-arch portion may be a dome shape, a quadrangularpyramidal shape, a circular conical shape (cone shape), etc. A foothaving a plantar-arch portion is disclosed in, for example, JapanesePatent Application No. 2002-037988 which is applied by the presentapplicant.

In the figure, reference numeral 1112 denotes a side edge (outer sideedge) or a side surface (outer side surface) which is remote from theother foot, reference numeral 1113 denotes a side edge (inner side edge)or a side surface (inner side surface) which is adjacent to the otherfoot, reference numeral 1114 denotes a side edge (front side edge) or aside surface (front side surface) at the front of the robot, andreference numeral 1115 denotes a side edge (rear side edge) or a sidesurface (rear side surface) at the rear of the robot.

As shown in the figure, all of the side surfaces 1112 to 1115 of themain foot body 1110 are flat, and all of the side edges 1112 to 1115 arelinear accordingly. In the case in which the grooves or the plantar-archportion which extends to the side edges 1112 to 1115 are formed in thefoot bottom surface, the side edges 1112 to 1115 include a curved lineor a discontinuous line corresponding to the shape of the grooves or theplantar-arch portion. However, it is only necessary that the shapes ofthe side edges 1112 to 1115 are linear lines when the side edges 1112 to1115 are projected onto a plane including the foot bottom surface of thefoot.

The adjacent side surfaces 1112 to 1115 of the main foot body 1110 areconnected to each other with smooth curved surfaces. In the presentexample, the curved surfaces are arc surfaces (R surfaces). In addition,the side surfaces 1112 to 1115 of the main foot body 1110 and the footbottom surface of the foot are also connected to each other with smoothcurved surfaces. The reason for connecting the surfaces (side surfacesand the foot bottom surface) with the smooth curved surfaces is toprevent stumbling, etc., caused when these portions are caught by, forexample, the surface having bumps and depressions.

FIG. 47 is a diagram for explaining the behavior of the foot accordingto the eleventh structure when the robot falls over. A state in whichthe robot is standing on one foot (right foot in this case) on the roadsurface is shown on the left in FIG. 47, where reference numeral 50denotes the gravity center of the robot. In addition, a state in whichthe balance of the robot is shifted to the right by, for example,receiving an external force in the horizontal direction (from the left)and the robot is starting to fall over is shown in on the right in FIG.47.

As shown on the right in FIG. 47, the robot starts to fall over byrotating around a line 51 including the outer side edge 1112 of the mainfoot body 1110, the line 51 serving as a reference of the falling motion(rotational center). Since the entire region of the outer side edge 1112is in line contact with the road surface, the possibility that the robotwill rotate around the yaw axis is extremely low. The above discussionalso applies to the cases where the robot falls over around the innerside edge 1113, the front side edge 1114, and the rear side edge 1115.

In the foot according to the eleventh structure, all of the sidesurfaces 1112 to 1115 of the main foot body 1110 are flat, and nooutward projections are provided thereon. Accordingly, when the robotfalls over, it rotates around one of the side edges 1112 to 1115.Therefore, the attitude and behavior of the robot in the falling motioncan be easily predicted.

A twelfth example of the foot 150 will be described below with referenceto FIGS. 48 and 49.

FIG. 48 is a plan view showing the schematic construction of the footaccording to a twelfth structure. Although FIG. 48 shows only one of thefeet attached to the left and right legs, the construction of the otherone of the feet is plane-symmetric to that of the foot shown in thefigure.

The foot according to the twelfth structure includes a main foot body1210 which is constructed of a rectangular plate-shaped member and whichis connected to the ankle 114 of the corresponding lower limb 110. Themain foot body 1210 is preferably composed of a material similar to thatused in the foot according to the eleventh structure.

A connector 1211 for providing connection to the ankle 114 is formedintegrally with the main foot body 1210 on the top surface of the mainfoot body 1210. In addition, the bottom surface (foot bottom surface) ofthe main foot body 1210 serves as the ground-contact surface. In thisexample, the foot bottom surface is flat.

The external shape of the foot bottom surface is shown in the figure. Inaddition, although not particularly limited, similar to the foot of theabove-described eleventh structure, a plurality of non-slip grooves or aplantar-arch portion having a concave shape may be formed in the footbottom surface.

In the figure, reference numeral 1212 denotes a side edge (outer sideedge) or a side surface (outer side surface) which is remote from theother foot, reference numeral 1213 denotes a side edge (inner side edge)or a side surface (inner side surface) which is adjacent to the otherfoot, reference numeral 1214 denotes a side edge (front side edge) or aside surface (front side surface) at the front of the robot, andreference numeral 1215 denotes a side edge (rear side edge) or a sidesurface (rear side surface) at the rear of the robot.

As shown in the figure, all of the side surfaces 1212 to 1215 of themain foot body 1210 are curved inward, and all of the side edges 1212 to1215 are also curved inward accordingly. In the case in which thegrooves or the plantar-arch portion which extends to the side edges 1212to 1215 are formed in the foot bottom surface, the side edges 1212 to1215 include a curved line or a discontinuous line obtained by combiningthe shape of the grooves or the plantar-arch portion and the shape ofthe corresponding side surface. However, it is only necessary that theshapes of the side edges 1212 to 1215 are inwardly curved lines when theside edges 1212 to 1215 are projected onto a plane including the footbottom surface of the foot.

Similar to the above-described first structure, the adjacent sides 1212to 1215 of the main foot body 1210 are connected to each other withsmooth curved surfaces, and the sides 1212 to 1215 and the foot bottomsurface are also connected to each other with smooth curved surfaces.

FIG. 49 is a diagram for explaining the behavior of the foot accordingto the twelfth structure when the robot falls over. A state in which therobot is standing on one foot (right foot in this case) on the roadsurface is shown on the left in FIG. 49, where reference numeral 60denotes the gravity center of the robot. In addition, a state in whichthe balance of the robot is shifted to the right by, for example,receiving an external force in the horizontal direction (from the left)and the robot is starting to fall over is shown in on the right in FIG.49.

As shown on the right in FIG. 49, the robot starts to fall over byrotating around a line 61 which connects two points which project moston the outer side edge 1212 of the main foot body 1210 at the front andrear of the outer side edge 1212, the line 61 serving as a reference ofthe falling motion (rotational center). Since the two points on theouter side edge 1212 are in contact with the road surface, thepossibility that the robot will rotate around the yaw axis is extremelylow. The above discussion also applies to the cases where the robotfalls over around the inner side edge 1213, the front side edge 1214,and the rear side edge 1215.

In the foot according to the twelfth structure, all of the side surfaces1212 to 1215 of the main foot body 1210 are curved inward. Accordingly,when the robot falls over, it rotates around the line which connect twopoints which project most on one of the outer side edges 1212 to 1215 atthe ends of the corresponding side edge. Therefore, the attitude andbehavior of the robot in the falling motion can be easily predicted.

Although all of the side surfaces 1212 to 1215 are curved inward in thisexample, the construction may also be such that only one or more of themis curved inward.

A thirteenth example of the foot 150 will be described below withreference to FIG. 50.

The foot according to a thirteenth structure is obtained by slightlymodifying the foot according to the above-described eleventh structure.FIG. 50 is a plan view showing the schematic construction of the footaccording to the thirteenth structure. Components similar to those ofthe above-described first structure are denoted by the same referencenumerals, and explanations thereof are thus omitted.

A foot 1310 is different from that described above in that notches 1322to 1325 are formed in the side surfaces 1112 to 1115, respectively, atcentral positions of the side surfaces 1112 to 1115. The notches 1322 to1325 extend from the top surface of the foot 1310 to the bottom surface(foot bottom surface) thereof. Other constructions are similar to thoseof the above-described structure. When the robot falls over, it rotatesaround one of the side edges 1112 to 1115 while the corresponding one ofthe side edges 1112 to 1115 is in contact with the road surface (atregions excluding the notches 1322 to 1325).

The reason why the notches 1322 to 1325 are provided is because if thereare small bumps or obstacles on the road surface when the robot fallsover, the possibility that the side edge which is in contact with theroad surface will be placed on the bumps or obstacles can be reduced byforming the notches 1322 to 1325. Accordingly, reduction inpredictability of the attitude and behavior of the robot in the fallingmotion can be prevented.

The shape of the notches 1322 to 1325 is not limited to that shown inthe figure, and may also be an arc shape or other shapes. In addition,it is not necessary that all of the side surfaces 1112 to 1115 beprovided with the notches 1322 to 1325, and the construction may also besuch that only one or more of them is provided with a notch.

A fourteenth example of the foot 150 will be described below withreference to FIG. 51.

The foot according to a fourteenth structure is obtained by slightlymodifying the foot according to the above-described twelfth structure.FIG. 51 is a plan view showing the schematic construction of the footaccording to the fourteenth structure. Components similar to those ofthe above-described second structure are denoted by the same referencenumerals, and explanations thereof are thus omitted.

A foot 1410 is different from that described above in that notches 1422to 1425 are formed in the side surfaces 1212 to 1215, respectively, atcentral positions of the side surfaces 1212 to 1215. The notches 1422 to1425 extend from the top surface of the foot 1410 to the bottom surface(foot bottom surface) thereof. Other constructions are similar to thoseof the above-described second structure. When the robot falls over, itrotates around an imaginary line (shown by a dotted chain line in thefigure) which connects two points which project most on one of sideedges 1212 to 1215 while the two points are in contact with the roadsurface.

The notches 1422 to 1425 are provided for a reason similar to that ofthe above-described foot according to the thirteenth structure. Theshape of the notches 1422 to 1425 is not limited to that shown in thefigure, and the notches 1422 to 1425 may also be formed similarly to thenotches 1322 to 1325 shown in FIG. 50. In addition, it is not necessarythat all of the side surfaces 1212 to 1215 be provided with the notches1422 to 1425, and the construction may also be such that only one ormore of them is provided with a notch.

Next, motion and characteristics of the foot (150 a to 150 c) of thelegged mobile robot 100 according to the present invention will bedescribed below with reference to FIGS. 52 to 61.

As shown in FIG. 52(A), in the foot 150 (150 a to 150 c) of the leggedmobile robot 100 according to the present embodiment, a concavity, suchas the plantar-arch portion 247, is formed in the bottom surface of thefoot 150, so that the ground-contact portions are always positioned atthe peripheral area of the foot 150. Accordingly, as shown in FIG.52(B), even when the weight is applied to the foot 150 at the centralposition thereof and the foot-sole mechanism is deformed or when theposition of the ZMP varies and deflection of the main foot body 160occurs as the legged mobile robot walks, variation in the position andthe shape of the ground-contact portions 245 is extremely small, andvariation in the resistive force against the moment about the yaw axiscan be reduced. More specifically, since the ground-contact portions areat the peripheral area of the foot 150 and reduction in the supportmoment can be reduced, unexpected change in the behavior of the robot,for example, spinning motion in which the robot rotates around theground-contact portions, can be prevented. Accordingly, a legged mobilerobot which has high attitude stability and which can continuouslyperform a stable motion can be obtained.

In addition, in the foot 150 of the legged mobile robot 100 according tothe present embodiment, when, for example, the foot 150 is placed on astep, as shown in FIG. 53, the edge of the step can be received by theplantar-arch portion 247, in particular, the second concavity 260, sothat the possibility that the foot-sole mechanism will be prevented frombeing directly affected can be increased. Accordingly, the walkingperformance of the legged mobile robot on the walking surfaces withbumps and depressions or steps can be improved and a legged mobilehaving robust characteristics can be obtained.

The foot 150 is also effective when the robot walks on a soft surface,such as a carpet, as shown in FIG. 54.

In general, carpets are soft and slippery, and it is difficult for thelegged mobile robot to walk on carpets since the moment around the yawdirection cannot be easily ensured and the support moment cannot beeasily increased. In addition, there is a risk that the foot will becaught by the surface and the falling moment will be generated dependingon the shape of the foot sole.

However, according to the foot 150 of the legged mobile robot 100according to the present embodiment, since the peripheral portion of thefoot sole has a smooth shape, the foot 150 can be prevented from beingcaught by fibers of the carpet. In addition, the fibers of the carpetare received by the concavity 180 such as the plantar-arch portion 247,so that suitable frictional force can be obtained and the moment aroundthe yaw direction can be generated and adjusted. In addition, when thefibers of the carpet are long enough to reach the flexible portion, thefriction generated between them serves as the support in the yawdirection. As a result, suitable braking force and impelling force canbe obtained and the robot can walk stably.

In addition, in the foot 150, the side surfaces 243 of the main footbody 240 and the ground-contact portions 245 are connected to each otherwith smooth curved surfaces (R surfaces) 244. Accordingly, theseportions can be prevented from being caught by the floor surface, thatis, a risk that the frictional force will be increased excessively andthe falling moment will be generated can be reduced, and the foot can bemoved smoothly, as shown in FIG. 55.

In addition, the foot 150 includes the flexible portion 270 in theconcavity such as the plantar-arch portion 247 of the main foot body240. As described above with reference to FIG. 53, the flexible portion270 deforms and receives a projection, such as a step, which enters theconcavity. In addition, the flexible portion 270 exerts a frictionalretaining force based on an adhesion force on the projection. Morespecifically, the flexible portion 270 adequately changes its shape so ato adapt itself to the state of the road surface.

For example, FIG. 56 shows a state in which the ceiling surface 261 ofthe second concavity 260 is in contact with a step. In this state, theflexible portion 270 adapt itself to the road surface and exerts africtional force, so that the foot 150 can be prevented from slippingand sliding down the step.

In particular, the case is considered in which the step is relativelylarge compared to the foot 150, as shown in FIG. 57, and the robot mustbe supported by the plantar-arch portion 247. In this case, although theflexible portion 270 first comes into contact with the step at aposition 271 on one side of the flexible portion 270, and then deformssuch that the contact area extends to a position 272. Accordingly, asupport polygon 273 has a trapezoidal shape, as shown in the figure. Asa result, the control stability region increases, and the stability ofcontrol can be improved.

FIGS. 58 and 59 show modifications of the flexible portion 270 in thecase in which a projection on the road surface reaches the flexibleportion 270. FIG. 58 shows the manner in which a standard flexibleportion 270 composed of a normal elastic material such as rubberdeforms. In this case, there is a limit to the support moment which canbe generated by the flexible portion 270. In contrast, when a materialwhich is more flexible and which can maintain the deformed state for acertain time, that is, a material having hysteresis characteristics, isused, the support moment can be increased, as shown in FIG. 59. When theflexible portion 270 deforms in the manner shown in the figure, thelegged mobile robot can be more safely supported even in places wherethere is a risk of sliding down, such as steps.

In addition, the foot 150 is also effective when the foot 150 steps onan obstacle which can roll, as shown in FIGS. 60 and 61. When a normalfoot steps on such an obstacle, the foot totters and moves like a seesawon the obstacle. Thus, the support moment cannot be generated and thebehavior of the foot becomes nonlinear. Accordingly, stability ofcontrol is reduced.

In comparison, when the flexible portion 270 is provided, the flexibleportion 270 is placed on the obstacle so as to enwrap it, as shown inFIG. 60, if the obstacle is small. Accordingly, the support point of thefoot sole can be ensured. In addition, even when the obstacle isrelatively large, a height h by which the foot sole is separated fromthe road surface is small. Thus, the factor of instability can bereduced.

In addition, since the obstacle is received by the flexible portion 270and is flexibly adapted to the bottom surface of the main foot body 260,the obstacle functions as if it is a part of the foot, and thepossibility that the extremely fast motion will occur or the robotcannot be controlled because of discontinuous, nonlinear motion thereofcan be largely reduced.

In addition, in the foot 150, the widths of the grooves 246 decreasetoward the side surfaces of the foot 150. In the case in which the robotmoves on a slippery road surface, such as a carpet, if the side surfaces262 of the grooves 246 are parallel to each other and the widths of thegrooves 246 are constant, the fibers of the carpet smoothly move insidethe plantar-arch portion 247 and do not exert a reaction force.

In comparison, when the side surfaces 262 are not parallel, as shown inFIG. 62, the fibers are collected between the side surfaces 262 andexert a reaction force. This reaction force serves as a frictionalretaining force, which is extremely effective when the robot is on thecarpet where the frictional force cannot be easily ensured.

In addition, in the foot 150, four grooves 246 are formed at the front,rear, left, and right positions of the foot 150 such that the grooves246 extend from the concavity at the central area to the outside.Accordingly, the motions, operations, and effects which are describedabove with reference to the figures can be obtained irrespective of thedirection in which the foot is moved, the angle at which the foot isplaced on the step, and the part of the foot which steps on an obstacle.Accordingly, a stable legged mobile robot with small factor ofinstability which can be stably controlled can be provided.

Support Structure of Instep and Foot Sole

A first example of a support structure of an instep (upper portion of afoot) and a foot bottom (sole of the foot) will be described below withreference to FIGS. 63 and 64. FIG. 63 is a side view of the foot andFIG. 64 is a sectional view of FIG. 63 cut along line A-A.

The foot according to the first structure includes an instep 1110 whichis connected to the ankle 114 of the corresponding lower limb 110 and afoot sole 1120 which directly comes into contact with the road surface,and has a two-part structure in which the foot sole 1120 is movablyattached to the instep 1110. The instep 1110 and the foot sole 1120 arepreferably composed of a light, strong material such as an aluminumalloy and a magnesium alloy.

The instep 1110 includes a rectangular outer frame 1111, a top platewhich covers the top side of the outer frame 1111, and a connector 1112which is disposed on the top plate. The connector 1112 is used forproviding connection to the ankle 114. Four side surfaces of the outerframe 1111 are provided with through holes for receiving fixing pins atthe central positions of the side surfaces. The holes for receiving thefixing pins are long holes which extend in the horizontal direction(X-axis direction and Y-axis direction).

The foot sole 1120 is constructed of a rectangular plate-shaped member,and the shape of the side surfaces of the foot sole 1120 is slightlysmaller than the shape of the inner surfaces of the outer frame 1111 ofthe instep 1110. The four side surfaces of the foot sole 1120 areprovided with holes for receiving the fixing pins at positionscorresponding to the holes for receiving the fixing pins formed in theouter frame 1111 of the instep 1110.

The foot sole 1120 is attached to the instep 1110 by inserting thefixing pins 1130 into the holes formed in the outer frame 1111 fromoutside while the foot sole 1120 is inserted into the outer frame 1111of the instep 1110 from below, fitting coil springs 1131 to end portionsof the fixing pins 1130, and press-fitting the end portions of thefixing pins 1130 into their respective holes formed in the foot sole1120.

In this state, the top surface of the foot sole 1120 faces the bottomsurface of the top plate of the instep 1110, and the side surfaces ofthe foot sole 1120 face their respective inner surfaces of the outerframe 1111 of the instep 1110 with predetermined gaps (allowance)therebetween. The coil springs 1131 through which the fixing pins 1130are inserted are disposed between the side surfaces of the foot sole1120 and the inner surfaces of the outer frame 1111 of the instep 1110in a compressed state. Accordingly, the foot sole 1120 can move intwo-axis directions (X-axis direction and Y-axis direction) along thebottom surface of the top plate of the instep 1110 (in the X-Y plane)within a range corresponding to the gaps (or an area corresponding tothe length of the holes in the side surfaces of the instep 1110).

Forces applied to the foot sole 1120 by the coil springs 1131 are setsuch that the foot sole 1120 is placed at the central position (neutralposition) inside the outer frame 1111 of the instep 1110 when noexternal force is applied to the foot sole 1120.

Although not shown in the figure, a plurality of force sensors fordetecting pressures in the Z-axis direction are provided on the bottomsurface of the foot sole 1120. These force sensors are used forcalculating the ZMP, and, in the present example, four force sensors aredisposed at four corners on the bottom surface of the foot sole 1120.

Each of these force sensors includes a metal diaphragm and four straingauges, and is constructed by forming a bridge circuit with the fourstrain gauges and laminating the stain gauges on the metal diaphragm.However, the force sensors are not limited to this, and those havingother constructions may also be used. In addition, the number of forcesensors for detecting the ZMP and the arrangement thereof are also notlimited to the above descriptions.

In addition, an acceleration sensor 1132 for detecting accelerations inthe X-axis direction and the Y-axis direction are mounted on the footsole 1120. The position at which the acceleration sensor 1132 isdisposed is not particularly limited. In the present embodiment, theacceleration sensor 1132 is disposed at the central position of the footsole 1120, as shown in FIG. 64. The output from the acceleration sensoris used for detecting the inclination of the road surface with respectto the direction of gravity or the stumbling motion caused by, forexample, bumps and depressions on the road surface.

In the above-described construction, the end portions of the fixing pins1130 are press-fitted into the holes formed in the foot sole 1120 inorder to attach the foot sole 1120 to the instep 1110 in a movablemanner. Alternatively, however, the end portions of the fixing pins 1130may also be screwed into the holes formed in the foot sole 1120 byforming male threads in the end portions of the fixing pins 1130 andfemale threads in the holes in the foot sole 1120. In addition, theconstruction may also be such that the fixing pins 1130 are fixed to theinstep 1110 by press-fitting or by means of screws and the holes forreceiving the fixing pins in the foot sole 1120 are formed as long holeswhich extend in the horizontal direction (X-axis direction and Y-axisdirection), so that the end portions of the fixing pins 1130 can slidein the holes in the X and Y directions. However, the construction formovably attaching the foot sole 1120 to the instep 1110 is not limitedto this, and various other constructions may also be used.

In addition, although the coil springs 1130 are used as buffer means inthe present example, the buffer means is not limited to this, and otherelastic members such as a leaf spring, other types of springs, or rubbermay also be used.

Since the foot sole 1120 is movably attached to the instep 1110, a timedelay is generated between the motion of the foot sole 1120 and that ofthe instep 1110 when the robot walks. In addition, since the coilsprings 1131 are placed between the foot sole 1120 and the instep 1110as the buffer means, when the idling leg is placed on the road surface,the reaction force from the road surface is slowly applied to the lowerlimb 100. Accordingly, the impact on the joints of the lower limb 110can be reduced and load on the actuators can also be reduced. Inaddition, the attitude stability of the robot with respect to fastoperations of the actuators which occurs when the robot is moved fastcan be improved. In addition, even when there are mechanical errors(displacements) in the driving system or when control errors occur, theymay be absorbed within the movable range of the foot sole 1120 and theirinfluence can be reduced.

In addition, since there is a time lag between the detection of thestumbling motion of the robot based on the output from the accelerationsensor 1132 provided on the foot sole 1120 and the time when the footsole 1120 reaches the end of its movable range with respect to theinstep 1110 and the impact is completely transmitted to the instep 1110,motion to avoid falling over can be performed during this time.Accordingly, the controllability of the robot's attitude and theattitude stability can be improved.

Since elastic means (coil springs 1130) is used as the buffer meansbetween the instep 1110 and the foot sole 1120, there is a risk in thatthe foot sole 1120 will continuously vibrate with respect to the instep1110 for a long time and the vibration will adversely affect thecontrollability of the walking motion. In such a case, viscous means(for example, a damper) is preferably provided along with the elasticmeans in order to improve the damping characteristics. In this case, theelasticity coefficient of the elastic member and the viscositycoefficient of the viscous member are preferably set such that thevibration of the foot sole 1120 which occurs when the foot sole 1120leaves the road surface in the walking motion of the leg is reduced to apredetermined extent before the foot sole 1120 is placed on the roadsurface again. Since the vibration of the foot sole 1120 is reduced to apredetermined extent at the time when the idling leg is placed on theground, it is not necessary for the robot's control system to re-performthe trajectory calculation and other calculations for control.Accordingly, the controllability can be improved. The above-describedpredetermined extent refers to a minimum necessary vibration which canbe tolerated while the control system of the robot achieves stablewalking motion.

A second example of a support structure of an instep (upper portion of afoot) and a foot bottom (sole of the foot) will be described below withreference to FIGS. 65 and 66. FIG. 65 is a side view of the foot andFIG. 66 is a sectional view of FIG. 4 cut along line B-B.

The foot of this example includes an instep 1210 which is connected tothe ankle 114 of the corresponding lower limb 110 and a foot sole 1220which directly comes into contact with the road surface, and has atwo-part structure in which the foot sole 1220 is movably attached tothe instep 1210. The instep 1210 and the foot sole 1220 are preferablycomposed of a light, strong material such as an aluminum alloy and amagnesium alloy.

The instep 1210 is constructed of a rectangular plate-shaped member, andfour side surfaces of the instep 1210 are provided with holes forreceiving fixing pins. In addition, a connector 1211 for providingconnection to the ankle 114 is formed integrally with the instep 1210 onthe top surface of the instep 1210.

The foot sole 1220 includes a rectangular outer frame 1221 and a bottomplate 1222 which covers the bottom side of the outer frame 1221. Theshape of the inner surfaces of the outer frame 1221 of the foot sole1220 is slightly larger than the shape of the side surfaces of theinstep 1210. The four side surfaces of the outer frame 1221 of the footsole 1220 are provided with through holes for receiving the fixing pinsat positions corresponding to the holes for receiving the fixing pinsformed in the side surfaces of the instep 1210. The holes for receivingthe fixing pins formed in the side surfaces of the foot sole 1220 arelong holes which extend in the horizontal direction (X-axis directionand Y-axis direction).

The foot sole 1220 is attached to the instep 1210 by inserting thefixing pins 1230 into the holes formed in the outer frame 1211 fromoutside while the instep 1210 is inserted into the outer frame 1211 fromabove, fitting coil springs 1231 to end portions of the fixing pins1230, and press-fitting the end portions of the fixing pins 1230 intotheir respective holes formed in the instep 1210.

In this state, the top surface of the bottom plate 1222 of the foot sole1220 faces the bottom surface of the instep 1210, and the inner surfacesof the outer frame 1221 of the foot sole 1220 face their respective sidesurfaces of the instep 1210 with predetermined gaps (allowances)therebetween. The coil springs 1231 through which the fixing pins 1230are inserted are disposed between the inner surfaces of the outer frame1221 of the foot sole 1220 and the side surfaces of the instep 1210 in acompressed state. Accordingly, the foot sole 1220 can move in two-axisdirections (X-axis direction and Y-axis direction) along the bottomsurface of the instep 1210 (in the X-Y plane) within a rangecorresponding to the gaps (or an area corresponding to the length of theholes in the side surfaces of the foot sole 1220).

Pressures applied to the foot sole 1220 by the coil springs 1231 are setsuch that the instep 1210 is placed at the central position (neutralposition) inside the outer frame 1221 of the foot sole 1220 when noexternal force is applied to the foot sole 1220.

Similar to the above-described first structure, force sensors forcalculating the ZMP and an acceleration sensor for detectingaccelerations in the X-axis direction and the Y-axis direction aremounted on the foot sole 1220. In addition, also in this example, thebuffer means is preferably constructed by combining elastic means andviscous means.

Advantages obtained by the above-described first structure can also beobtained by this structure. In addition, since the outer frame 1221 ofthe foot sole 1220 is constructed so as to cover the side surfaces ofthe instep 1210, the impact which occurs when one of the side surfacesof the foot strikes an obstacle can be reduced.

A third example of a support structure of an instep (upper portion of afoot) and a foot bottom (sole of the foot) will be described below withreference to FIGS. 67 and 68. FIG. 67 is a plan view of the foot andFIG. 68 is a partially broken side view of the foot.

The foot according to the third structure includes an instep 1310 whichis connected to the ankle 114 of the corresponding lower limb 110 and afoot sole 1320 which directly comes into contact with the road surface,and has a two-part structure in which the foot sole 1320 is movablyattached to the instep 1310.

The instep 1310 is constructed of a rectangular plate-shaped member anda connector 1311 for providing connection to the ankle 114 is formedintegrally with the instep 1310 on the top surface of the instep 1310.Although not shown in the figure, a plurality of force sensors fordetecting pressures in the Z-axis direction which are used forcalculating the ZMP are provided on the bottom surface of the instep1310. More specifically, four force sensors are disposed at four cornersof the bottom surface of the instep 1310.

Each of these force sensors includes a metal diaphragm and four straingauges, and is constructed by forming a bridge circuit with the fourstrain gauges and laminating the stain gauges on the metal diaphragm.However, the force sensors are not limited to this, and those havingother constructions may also be used.

The foot sole 1320 is a rectangular box-shaped member with an open topwhich includes a bottom plate 1321 and upright side plates 1322 whichare formed integrally with the bottom plate 1321 along the peripheralsides of the bottom plate 1321. The top surface of the bottom plate 1321is in contact with the bottom surface of the instep 1310. In addition,the bottom surface of the bottom plate 1321 serves as the foot bottomsurface of the foot 150. The bottom surface of the bottom plate 1321 andouter surfaces of the side plates 1322 are connected to each other withR surfaces (arc surfaces) or smooth curved surfaces.

The internal shape of the side plates 1322 of the foot sole 1320 issimilar to the shape of side surfaces of the instep 1310, but isslightly larger. The side surfaces of the instep 1310 face the innersurfaces of the side plates 1322 of the foot sole 1320 with small gaps(allowances) therebetween. Accordingly, the foot sole 1320 can moverelative to the instep 1310 along the bottom surface of the instep 1310,that is, in an arbitrary direction in the X-Y plane.

The foot sole 1320 is attached to the instep 1310 with a retainingmechanism (not shown) in such a manner that the foot sole 1320 does notfall from the instep 1310 when the corresponding leg is off the roadsurface and the movement of the foot sole 1320 in the X-Y plane is notrestricted. The retaining mechanism preferably has a mechanism foreasily attaching/detaching the foot sole 1320 when the foot sole 1320 isto be replaced.

A buffer (buffer means) 1330 is disposed between the side plates 1322 ofthe foot sole 1320 and the side surfaces of the instep 1310. Forexample, an endless rubber sheet may be used as the buffer 1330, and bedisposed such that gaps between the inner surfaces of the side plates1322 of the foot sole 1320 and the side surfaces of the instep 1310 arecompletely filled with the rubber sheet. However, the buffer is notlimited to this, and a leaf spring, a sponge, a solid or semi-solidviscous means may also be used.

In addition, the inner surfaces of the side plates 1322 of the foot sole1320 and the side surfaces of the instep 1310 may be adhered to eachother in the process of assembling the foot by filling the gaps betweenthem with an adhesive which shows elasticity and/or viscosity in a curedor solid state. In such a case, foreign matter can be prevented fromentering the gaps, and effects of the retaining mechanism for movablyattaching the foot sole 1320 on the foot sole 1310 can be obtainedwithout using one.

According to this structure, the foot sole 1320 can move in an arbitrarydirection relative to the instep 1310 along the bottom surface of theinstep 1310, and restriction on the moving direction is less compared tothe above-described first and second structures.

The above-described buffer is preferably formed such that the gapsbetween the inner surfaces of the side plates 1322 of the foot sole 1320and the side surfaces of the instep 1310 are completely filled sinceforeign matter can be prevented from entering the gaps in such a case.However, the present invention is not limited to this, and a pluralityof buffers may be arranged with gaps therebetween. In addition, it isnot necessary that the buffer be provided, and the buffer may also beomitted.

Connection/Replacement Structure of Leg and Foot at Ankle

Next, a connection structure of a leg and a foot and a replacementstructure of the foot at an ankle of the legged mobile robot will bedescribed below.

A first example of a connection structure of a leg and a and areplacement structure of the foot at an ankle of the legged mobile robotwill be described below with reference to FIGS. 69 and 70.

FIG. 69 is a sectional view of a foot 150 and connecting parts between alower limb (movable leg) 110 and the foot 150.

A leg-mounted connecting part 1001 which is provided on the ankle 114 ofthe lower limb 110 includes a connection/positioning projection 1002 anda connector 1003 for providing electrical connection. In addition, anotch 1004 is formed in a side surface of the connection/positioningprojection 1002.

In addition, a connecting part 1102 which is provided on a main footbody 1101 of the foot 150 at the upper side of the main foot body 1101includes a connection/positioning concavity 1102, a connector 1103 forproviding electrical connection, a container 1104 for accommodating theconnector 1103, and a connection actuator 1105.

A positioning pin 1106 is attached to an end of the connection actuator1105 in such a manner that the positioning pin 1106 can move forward andbackward (in the X-axis direction) along the bottom surface of theconnection/positioning concavity 1102. When the positioning pin 1106projects into the connection/positioning concavity 1102, it is fitted inthe notch 1004 formed in the side surface of the connection/positioningprojection 1002. In the state shown in FIG. 69, the positioning pin 1106is retracted by the connection actuator 1105 so that theconnection/positioning projection 1002 can be inserted into and removedfrom the connection/positioning concavity 1102.

FIG. 70 is a sectional view of the connecting parts in the state inwhich the main foot body 1101 is attached to the leg-mounted connectingpart 1001.

The main foot body 1101 is strongly connected to the leg-mountedconnecting part 1001 by pushing out the positioning pin 1106 by theconnection actuator 1105 and fitting an end portion of theconnection/positioning projection 1002 into the notch 1004 while theconnection/positioning projection 1002 is completely fitted in theconnection/positioning concavity 1102.

At this time, the connector 1003 is inserted into the container 1104 andis mechanically engaged with the connector 1103 which is disposed at thebottom of the container 1104, and terminals of the connector 1003 andtheir respective terminals of the connector 1103 are electricallyconnected to each other. Accordingly, electric power can be suppliedfrom the leg, that is, from the robot's main body, to the main foot body1101 and control commands and other data signals can be communicatedbetween them.

A concavity 1111 is formed in the bottom surface of theconnection/positioning concavity 1102 of the main foot body 1101, and anelectrical circuit substrate 1112 is disposed in the concavity 1111. Theelectrical circuit substrate 1112 includes the ROM 305 (see FIG. 3)which serves as memory means which stores various data and other relatedcircuits, and the main control unit 300 of the robot's main body canaccess the ROM 305 via the connectors 1103 and 1003 and the bus 304. Inaddition, the electrical circuit substrate 1112 also includes signalprocessing circuits for various sensors provided on the main foot body1101.

Although not shown in the figure, force sensors and an accelerationsensor are also provided on the main foot body 1101. More specifically,a plurality of force sensors for detecting pressures in the Z-axisdirection are provided on the ground-contact portion on the bottom ofthe main foot body 1101. These force sensors are used for calculatingthe ZMP, and, in the present example, four force sensors are disposed atfour corners of the bottom surface (foot bottom surface) of the mainfoot body 1101.

Each of these force sensors includes a metal diaphragm and four straingauges, and is constructed by forming a bridge circuit with the fourstrain gauges and laminating the stain gauges on the metal diaphragm.However, the force sensors are not limited to this, and those havingother constructions may also be used. In addition, the number of forcesensors for detecting the ZMP and the arrangement thereof are also notlimited to the above descriptions.

In addition, an acceleration sensor for detecting accelerations in theX-axis direction and the Y-axis direction are also mounted on the mainfoot body 1101. Although the position at which the acceleration sensoris disposed is not particularly limited, it is disposed in the concavity1111 in the present example. The output from the acceleration sensor isused for detecting the inclination of the road surface with respect tothe direction of gravity or the stumbling motion caused by, for example,bumps and depressions on the road surface. Output signals from thesesensors are transmitted to the main control unit 300 of the robot's mainbody via processing circuits on the electrical circuit substrate 1112,the connectors 1103 and 1003, and the bus 304.

The ROM 305 mounted on the electrical circuit substrate 1112 stores footinformation described below as information related to the main foot body1101.

The foot information includes information identical to the correspondingmain foot body 1101 which is necessary for the main control unit 300 toperform the trajectory calculation and other calculations. Morespecifically, the foot information includes foot identificationinformation, foot structure information, foot sensor information, etc.

The foot identification information is identification information (ID)used for distinguishing the corresponding main foot body 1101 from othermain foot bodies. The foot structure information includes the dimensions(shape), the material, the weight, the coefficient of friction of aground-contact surface, etc., of the main foot body and its structuralmembers. In the foot structure information, the shape of the foot bottomsurface (sole shape) of the main foot body 1101 including theground-contact portion which comes into contact with the road surface isparticularly important for the control calculation. This shape isexpressed in the form of a mathematical formula (two dimensionalapproximate formula) or by bitmap format.

The foot sensor information is information related to various sensorsprovided on the main foot body 1101, and includes identificationinformation (ID for distinguishing the corresponding sensors from othersensors), the number, the arrangement, and the characteristics of thesensors. Since the force sensors for detecting the ZMP and theacceleration sensor for detecting collision or the inclination of theroad surface are provided on the main foot body 1101, sensor informationrelated to these sensors is stored. In addition, other sensors, forexample, contact sensors for determining whether or not the foot bottomsurface is placed on the road surface, sensors for detecting thedisplacement (slipping) of the foot bottom surface placed on the roadsurface with respect to the road surface, etc., may also be provided. Inthis case, sensor information for each of the sensors is stored.

Although the ROM in which data cannot be overwritten is used as thememory means for storing the foot information in this case, an EPROM, aSRAM, a DRAM with a backup power source, etc., in which data can beoverwritten may be used as the memory means. In such a case, dynamicallychanging information may also be stores as the foot information, and beupdated as necessary. For example, log information showing the variationin the characteristics of the sensors over time may also be stored asthe foot information.

In addition to the above-described information, other variousinformation related to the corresponding main foot body 1101 may also bestored as the foot information. In addition, information which is notdirectly related to the corresponding main foot body 1101 may also bestored.

The foot information stored in the memory means provided on the mainfoot body 1101 is read out by the CPU 301 of the main control unit 300of the robot's main body via the bus 304, etc., when the main foot body1101 is connected to the ankle 114 of the lower limb 110 in the processof replacing the main foot body 1101, etc., when the legged mobile robotis initialized (when the power is turned on or when the robot is reset),or at other suitable time. Then, the foot information is used by themain control unit 300 for various control calculations includingcalculations for obtaining commands supplied to each of the actuators306.

Since the main foot body 1101 includes the ROM as the memory means forstoring the foot information related to the main foot body 1101, it isnot necessary that the memory means (the ROM 303, the RAM 302, and otherexternal memories) included in the main control unit 300 store theinformation related to the main foot body 1101. Accordingly, the numberof memories or the capacity of the memory used as the memory means canbe reduced. Alternatively, the memory area which has been used forstoring this information can be used for storing other information.

In addition, when various kinds of main foot bodies which have differentsole shapes and numbers and kinds of sensors suitable for various statesof road surfaces, and which store their foot information, are preparedand are replaced as necessary, it is not necessary to input the footinformation manually, or by other means, each time the main foot bodiesare replaced.

The foot information stored in the memory means of the main foot bodymay include only the foot identification information, or only the footidentification information and other main information (for example, theshape of the foot sole). In such a case, the remaining information suchas the foot structure information and the foot sensor information arestored in the memory of the main control unit 300 in correspondence withthe foot identification information. When the main foot body isconnected to the ankle, the foot identification information is read outand is used for obtaining the corresponding foot structure information,the foot sensor information, etc. Also in this case, the task ofmanually inputting the identification information of the foot when thefoot is replaced is not necessary, and the task of replacing the footcan be facilitated.

A second example of a connection structure of a leg and a foot and areplacement structure of the foot at an ankle of the legged mobile robotwill be described below with reference to FIG. 71.

In this example shown in the figure, the foot is replaced by using anactuator which is necessarily included in the legged mobile robot.Generally, legged mobile robots including human-shaped robots have aplurality of joints, that is, a plurality of degrees of freedom.Accordingly, by utilizing these degrees of freedom, the necessity ofproviding an actuator exclusively used for fixing the foot can beeliminated. More specifically, when a mechanism for fixing the foot isoperated autonomously by using the motion of the componentscorresponding to the arms and hands of human beings, it is not necessaryto use an exclusive actuator.

FIG. 71 includes a top view (A), a side view (B), a back view (C), and asectional side view (D) showing a mechanism for fixing a foot which isfree from an exclusive actuator in a state in which the foot is releasedfrom the ankle.

A main foot body 1201 includes a connection/positioning concavity 1202,a foot-mounted electrical connector 1203, and a container 1204 foraccommodating the connector 1203 at the bottom of the container 1204.

In addition, a holder 1205, a fixing pin 1206, an operation lever 1207,and a compression spring 1208 are provided on the main foot body 1201 asshown in the figure.

In the state shown in FIG. 71, the fixing pin 1206 is urged by thecompression spring 1208 to apply pressure toward theconnection/positioning concavity 1202. Since the operation lever 1207,which is formed integrally with the fixing pin 1207, is pushed along alever guide groove 1209, the fixing pin 1206 does not move from theposition shown in the figure. When the main foot body 1201 is in thisstate, the robot can replace the main foot body 1201.

In addition, FIG. 72 shows the state in which the foot is fixed. In thestate shown in the figure, the operation lever 1207 is moved along thelever guide groove 1209 in the direction to fix the foot, and the fixingpin 1206 is urged by the compression spring 1208 to project into theconnection/positioning concavity 1202. In addition, an end portion ofthe fixing pin 1206 is fitted into a notch 1004 formed in a leg-mountedconnecting part 1001. Accordingly, the main foot body 1201 is stronglyconnected to the leg-mounted connecting part 1001.

By performing the operation of moving the operation lever 1207 describedabove with reference to FIGS. 71 and 72 by using the arm and hand of therobot, the robot can autonomously fix and release the foot for replacingthe foot.

In addition, in the case in which the robot is required to adapt itselfto various kinds of road surfaces, it is effective if the robot performslegged motion while carrying one or more pairs of feet (spare). Inaddition, in the case in which the robot walks on an unknown roadsurface, there is a possibility that its feet must be replaced foradapting itself to the road surface. For example, when the robot is usedin severe work environments for, for example, disaster relief orplanetary exploration, it is rarely possible to specify the kind of theroad surface. However, the use of robots is strongly expected in such anextreme and severe work environment.

In addition, although not shown in the figure, the main foot body 1201includes an electrical circuit substrate similar to the electricalcircuit substrate 1112 shown in FIGS. 69 and 70 which includes the ROM305 shown in FIG. 3, and the above-described foot information is storedin the ROM 305.

A third example of a connection structure of a leg and a foot and areplacement structure of the foot at an ankle of the legged mobile robotwill be described below with reference to FIGS. 73 and 74. FIG. 73 is asectional side view, and FIG. 74 is a block diagram showing a footcontrol unit.

The feet 150 according to the above-described first and secondstructures include the main foot bodies 1101 and 1201, respectively, andeach of the main foot bodies 1101 and 1201 includes a foot sole whichdirectly comes into contact with the road surface. In comparison, a foot150 of this example includes an instep 1310 which is connected to theankle 114 of the corresponding lower limb 110 and a foot sole 1320 whichdirectly comes into contact with the road surface, and has a two-partstructure in which the foot sole 1320 is movably attached to the instep1310.

The instep 1310 is constructed of a rectangular plate-shaped member anda connector 1311 for providing connection to the ankle 114 is formedintegrally with the instep 1310 on the top surface of the instep 1310.The instep 1310 is detachably attached to the ankle 114 by fixing theinstep 1310 to the ankle 114 with screws or by other fixing means, or byusing a connecting mechanism similar to the above-described connectingmechanisms for connecting the main foot bodies 1101 and 1201. Aconcavity 1312 is formed in the bottom surface of the instep 1310, andan instep circuit unit (instep circuit substrate) 2100 is attached tothe concavity 1312 with a supporter 1313 therebetween.

Although not shown in the figure, a plurality of force sensors fordetecting pressures in the Z-axis direction which are used forcalculating the ZMP are provided on the bottom surface (surface aroundthe concavity 1312) of the instep 1310. In the present example, fourforce sensors are disposed at four corners of the bottom surface of theinstep 1310. Each of these force sensors includes a metal diaphragm andfour strain gauges, and is constructed by forming a bridge circuit withthe four strain gauges and laminating the stain gauges on the metaldiaphragm. However, the force sensors are not limited to this, and thosehaving other constructions may also be used.

In addition, an acceleration sensor for detecting accelerations in theX-axis direction and the Y-axis direction are mounted on the instep1310. The output from the acceleration sensor is used for detecting theinclination of the road surface with respect to the direction of gravityor the stumbling motion caused by, for example, bumps and depressions onthe road surface.

The foot sole 1320 is a rectangular box-shaped member with an open topwhich includes a bottom plate 1321 and upright side plates 1322 whichare formed integrally with the bottom plate 1321 along the peripheralsides of the bottom plate 1321. The top surface of the bottom plate 1321is in contact with the bottom surface of the instep 1310. In addition,the bottom surface of the bottom plate 1321 serves as the foot bottomsurface of the foot 150. The bottom surface of the bottom plate 1321 andouter surfaces of the side plates 1322 are connected to each other withR surfaces (arc surfaces) or smooth curved surfaces.

The internal shape of the side plates 1322 of the foot sole 1320 issimilar to the shape of side surfaces of the instep 1310, but isslightly larger. The side surfaces of the instep 1310 face the innersurfaces of the side plates 1322 of the foot sole 1320 with small gaps(allowances) therebetween. Accordingly, the foot sole 1320 can moverelative to the instep 1310 along the bottom surface of the instep 1310,that is, in an arbitrary direction in the X-Y plane.

The foot sole 1320 is attached to the instep 1310 with a retainingmechanism (not shown) in such a manner that the foot sole 1320 does notfall from the instep 1310 when the corresponding leg is off the roadsurface and the movement of the foot sole 1320 in the X-Y plane is notrestricted. The retaining mechanism has a mechanism for easilyattaching/detaching the foot sole 1320 when the foot sole 1320 is to bereplaced.

A buffer (buffer means or urging means) 1330 is disposed between theside plates 1322 of the foot sole 1320 and the side surfaces of theinstep 1310. In this example, an endless rubber sheet is used as thebuffer 1330, and is disposed such that gaps between the inner surfacesof the side plates 1322 of the foot sole 1320 and the side surfaces ofthe instep 1310 are filled with the rubber sheet. However, the buffer1330 is not limited to this, and a leaf spring, a sponge, a solid orsemi-solid viscous component may also be used.

In addition, the inner surfaces of the side plates 1322 of the foot sole1320 and the side surfaces of the instep 1310 may be adhered to eachother in the process of assembling the foot 150 by filling the gapsbetween them with an adhesive which shows elasticity and/or viscosity ina cured or solid state. In such a case, foreign matter can be preventedfrom entering the gaps, and effects of the retaining mechanism formovably attaching the foot sole 1320 on the foot sole 1310 can beobtained without using one.

The buffer 1330 is preferably formed such that the gaps between theinner surfaces of the side plates 1322 of the foot sole 1320 and theside surfaces of the instep 1310 are completely filled since foreignmatter can be prevented from entering the gaps in such a case. However,the present invention is not limited to this, and a plurality of buffersmay be arranged with gaps therebetween. In addition, it is not necessarythat the buffer be provided, and the buffer may also be omitted.

A foot-sole circuit unit (foot-sole circuit substrate) 2200 is attachedto the top surface of the foot sole 1320 with a supporter 1323therebetween so that the foot-sole circuit unit 2200 faces the instepcircuit unit 1313 disposed in the concavity 1312 of the instep 1310 witha gap therebetween.

As shown in FIG. 9, the instep circuit unit 2100 includes a power supplyunit 2101, an instep transmitter/receiver 2102, an instep controller2103, and an antenna 2105.

The power supply unit 2101 converts electric power supplied from therobot's main body into electromagnetic waves and supplies theelectromagnetic waves to the foot-sole circuit unit 2200 via the antenna2105. The instep transmitter/receiver 2102 transmits control signals andother signals to the foot-sole circuit unit 2200 from the antenna 2105,and receives control signals and other signals transmitted from thefoot-sole circuit unit 2200 through the antenna 2105. The instepcontroller 2103 includes a CPU and a memory (a RAM, a ROM, etc.), andcommunicates with the main control unit 300 of the robot's main body viathe bus 304. The ROM stores, for example, a ZMP calculation program, aroad-surface inclination angle determination program, stumbling-motiondetection program, etc. In this example, the instep circuit unit 2100 isused in place of the foot-mounted ROM 305 in FIG. 3.

In addition, as shown in FIG. 74, the foot-sole circuit unit 2200includes a power supply unit 2201, a foot-sole transmitter/receiver2202, a foot-sole controller 2203, a foot-sole information memory(memory), and an antenna 2205.

The power supply unit 2201 receives the electromagnetic wavestransmitted from the power supply unit 2101 through the antennas 2105and 2205, converts the electromagnetic waves into electric power, andsupplies the electric power to each part of the foot-sole circuit unit2100.

The foot-sole transmitter/receiver 2202 transmits control signals andother signals to the instep circuit unit 2100 from the antenna 2205, andreceives control signals and other signals transmitted from the instepcircuit unit 2200 through the antenna 2205. The foot-sole controller2203 includes a CPU and a memory (a RAM, a ROM, etc.), and communicateswith the instep controller 2102 via the foot-sole transmitter/receiver2202, the antennas 2205 and 2105, and the instep transmitter/receiver2102. The ROM stores, for example, a ZMP calculation program, aroad-surface inclination angle determination program, stumbling-motiondetection program, etc.

The foot-sole information memory 2204 is memory means which storesfoot-sole information. The foot-sole information memory 2204 stores thefoot-sole information described below as information related to the footsole.

The foot-sole information includes information identical to thecorresponding foot sole which is necessary for the main control unit 300to perform the trajectory calculation and other calculations. Morespecifically, the foot-sole information includes foot-soleidentification information, foot-sole structure information, foot-solesensor information, etc.

The foot-sole identification information is identification information(ID) used for distinguishing the corresponding foot sole 1320 from otherfoot soles. The foot-sole structure information includes the dimensions(shape), the material, the weight, the coefficient of friction of aground-contact surface, etc., of the foot sole 1320 and its structuralmembers. In the foot-sole structure information, the shape of the bottomsurface (sole shape) of the foot sole 1320 including the ground-contactportion which comes into contact with the road surface is particularlyimportant for the control calculation. This shape is expressed in theform of a mathematical formula (two dimensional approximate formula) orby bitmap format.

The foot-sole sensor information is information related to varioussensors provided on the main foot sole 1320, and includes identificationinformation (ID for distinguishing the corresponding sensors from othersensors), the number, the arrangement, and the characteristics of thesensors. In the present example, the force sensors for detecting the ZMPand the acceleration sensor for detecting collision or the inclinationof the road surface are provided on the instep 1310. However, thesesensors may also be provided on the foot sole 1320. In such a case,information related to these sensors is stored. In addition, othersensors, for example, contact sensors for determining whether or not thefoot bottom surface is placed on the road surface, sensors for detectingthe displacement (slipping) of the bottom surface placed on the roadsurface with respect to the road surface, etc., may also be provided onthe foot sole 1320. In this case, sensor information for each of thesensors is stored.

The foot-sole information memory 2204 may be a ROM in which data cannotbe overwritten or an EPROM, a SRAM, a DRAM with a backup power source,etc., in which data can be overwritten. When memory means in which datacan be overwritten is used, dynamically changing information may also bestored as the foot-sole information, and be updated as necessary. Forexample, log information showing the variation in the characteristics ofthe sensors over time may also be stored as the foot information.

In addition to the above-described information, other variousinformation related to the foot sole 1320 may also be stored as thefoot-sole information. In addition, information which is not directlyrelated to the foot sole 1320 may also be stored.

The foot-sole information stored in the foot-sole information memory2204 is read out by the main control unit 300 of the robot's main bodywhen the foot sole 1320 is connected to the instep 1310 in the processof replacing the instep 1310, etc., when the legged mobile robot isinitialized (when the power is turned on or when the robot is reset), orat other suitable time. More specifically, the main control unit 300commands the instep controller 2103 to read out the foot-soleinformation, and the instep controller 2103 commands the foot-solecontroller 2203 to read out the foot-sole information via the insteptransmitter/receiver 2102, the antennas 2105 and 2205, and the foot-soletransmitter/receiver 2202. The foot-sole controller 2203 reads outnecessary foot-sole information from the foot-sole information memory2204 and transmits the foot-sole information to the instep controller2103, and the instep controller 2103 transmits the foot-sole informationto the main control unit 300. The foot-sole information is used by themain control unit 300 for various control calculations includingcalculations for obtaining command values supplied to each of theactuators 306.

Since the foot sole 1320 includes the memory means (foot-soleinformation memory 2204) which stores the foot-sole information relatedto the foot sole 1320, it is not necessary that the memory means (theROM 303, the RAM 302, and other external memories) included in the maincontrol unit 300 store the information related to the foot sole 1320.Accordingly, the number of memories or the capacity of the memory usedas the memory means can be reduced. Alternatively, the memory area whichhas been used for storing this information can be used for storing otherinformation.

In addition, when various kinds of foot soles which have different soleshapes and numbers and kinds of sensors suitable for various states ofroad surfaces, and which store their foot-sole information, are preparedand are replaced as necessary, it is not necessary to input thefoot-sole information manually, or by other means, each time the footsoles are replaced.

The foot-sole information stored in the foot-sole information memory2204 may include only the foot-sole identification information, or onlythe foot-sole identification information and other main information (forexample, the shape of the foot sole). In such a case, the remaininginformation such as the foot-sole structure information and thefoot-sole sensor information are stored in a memory included in theinstep controller 2103 in correspondence with the foot-soleidentification information. When the foot sole 1320 is connected to theinstep 1310, the foot-sole identification information is read out and isused for obtaining the corresponding foot structure information, thefoot sensor information, etc., from the memory in the instep controller2103. Then, the thus obtained information is transmitted to the maincontrol unit 300.

In this example, data communication and power supply between the instepcircuit unit 2100 and the foot-sole circuit unit 2200 are performedwithout contact (by wireless communication) using electromagnetic waves.However, the instep circuit unit 2100 and the foot-sole circuit unit2200 may also be directly connected to each other with a flexible cable.In such a case, the kind and the attachment structure of the cable arepreferably selected such that the movement of the foot sole 1320relative to the instep 1310 is not impeded.

A fourth example of a connection structure of a leg and a foot and areplacement structure of the foot at an ankle of the legged mobile robotwill be described below with reference to FIGS. 75 to 78. FIG. 75 is apartially exploded side view, FIG. 76 is a plan view, FIG. 77 is apartially exploded sectional view, and FIG. 78 is a bottom view.

Similarly to the above-described third structure, a foot 150 of thisexample includes an instep 1410 which is connected to the ankle 114 ofthe corresponding lower limb 110 and a foot sole 1420 which directlycomes into contact with the road surface, and has a two-part structurein which the foot sole 1420 is movably attached to the instep 1410.

The instep 1410 is a rectangular box-shaped member with an open bottomwhich includes a top plate 1411 and upright side plates 1412 which areintegrally formed with the top plate 1411 along the peripheral sides ofthe top plate 1411. A connector 1413 for providing connection to theankle 114 is formed integrally with the top plate 1411 on the topsurface of the top plate 1411. The top plate 1411 is provided with screwholes (four screw holes are provided in this example) 1414 for attachingthe foot sole 1420. The outer side surfaces of the side plates 1412 areconnected to each other with R surfaces (arc surfaces) or smoothsurfaces. The instep 1410 is attached to the ankle 114 with screws or byother fixing means. Alternatively, the instep 1410 may also bedetachably attached to the ankle 114 by a connecting mechanism similarto the above-described connecting mechanisms for connecting the mainfoot bodies 1101 and 1201. In addition, an instep circuit unit (instepcircuit substrate) 2100 is attached to the bottom surface of the topplate 1411 of the instep 1410 at the central area thereof.

Although not shown in the figure, four projective sensor bases areformed integrally with the top plate 1411 of the instep 1410 on thebottom surface of the top plate 1411 at four corners thereof. Aplurality of force sensors for detecting pressures in the Z-axisdirection which are used for calculating the ZMP are provided on thesensor bases. Each of these force sensors includes a metal diaphragm andfour strain gauges, and is constructed by forming a bridge circuit withthe four strain gauges and laminating the stain gauges on the metaldiaphragm. However, the force sensors are not limited to this, and thosehaving other constructions may also be used.

In addition, an acceleration sensor (not shown) for detectingaccelerations in the X-axis direction and the Y-axis direction isprovided on the bottom surface of the top plate 1411 of the instep 1410.The output from the acceleration sensor is used for detecting theinclination of the road surface with respect to the direction of gravityor the stumbling motion caused by, for example, bumps and depressions onthe road surface.

The foot sole 1420 has a two-part structure in which a contact member1422 composed of a rectangular-plate shaped member is attached to thebottom surface of a foot-sole main body 1421 by adhesion or by means ofscrews.

The external shape of the foot-sole main body 1421 is approximately thesame as the external shape of the side plates 1412 at the open side ofthe instep 1410. In addition, a rectangular step portion 1423 is formedintegrally with the foot-sole main body 1421. The external shape of thestep portion 1423 is similar to the internal shape of the side plates1412 at the open side of the instep 1410, but is slightly smaller.

In order to attach the foot-sole main body 1421 to the instep 1410,fixing projections 1424 which project upward are formed on the topsurface of the foot-sole main body 1421 at positions corresponding tothe screw holes 1414 formed in the top plate 1411. The fixingprojections 1424 have columnar concavities 1425 for receiving buffers1430 at the lower sides thereof. In addition, the fixing projections1424 are provided with through holes 1426 which extend through thefixing projections 1424 in the vertical direction at projecting endsthereof. In addition, although not shown in the figure, sensor-pressingbases are formed integrally with the foot-sole main body 1421 atpositions corresponding to the ZMP sensors provided on the sensor basesformed on the top surface of the instep 1410 in such a manner that thesensor-pressing bases are pressed against or in contact with the ZMPsensors.

The external shape of the contact member 1422 is approximately the sameshape as that of the foot-sole main body 1421, and through holes 1427are formed in the contact member 1422 at positions corresponding to theconcavities 1425 of the foot-sole main body 1421. In order to reduce theimpact which occurs when the foot 150 is placed on the road surface, thecontact member 1422 is composed of, for example, a rubber sheet. Fromthe viewpoint of adaptability to the state of the road surface, thematerial of the contact member 1422 may be metal, plastic, or othermaterials instead of the rubber sheet. In addition, from the viewpointof adaptability to the state of the road surface, the bottom surface(ground-contact surface) of the contact member 1422 may have grooves, aplantar arch, etc. By suitably changing or selecting the material of thecontact member 1422 and the shape of the ground-contact surface, variouskinds of foot soles 1420 suitable for various states of road surfacescan be obtained.

The foot sole 1420 can be attached to the instep 1410 by inserting thestep portion 1423 of the foot-sole main body 1421 into the opening ofthe instep 1410 while the cylindrical buffers 1430 are fitted in theconcavities 1425 and the through holes 1427 in the foot sole 1420,inserting screws 1431 through the through holes formed in the buffers1430 and the through holes 1426 formed in the fixing projections 1424,and screwing end portions of the screws 1431 into the screw holes 1414formed in the top plate 1411.

At this time, the ZMP sensors (not shown) attached to the sensor bases(not shown) provided on the bottom surface of the top plate 1411 ispressed against by the end surfaces of the sensor-pressing bases (notshown) provided on the foot sole 1420, so that suitable preload isapplied to the ZMP sensors. Cylindrical elastic rubber members, coilsprings, etc., may be used as the buffers 1430. The buffers 1430 serveto reduce the impact transmitted to the instep 1410 from the foot sole1420 during the walking motion, as well as to suppress the vibration ofthe foot sole 1420 so that noise can be reduced and controllability canbe improved. In addition, the buffers 1430 also serve to maintain thestate that the foot sole 1420 can move relative to the instep 1410 alongthe Z-axis direction and in the X-Y plane. The buffer 1430 may also haveviscosity in addition to elasticity.

Another buffer may be disposed between the step portion 1423 of thefoot-sole main body 1421 and the inner surfaces of the side plates 1412of the instep 1410. In such a case, an endless rubber sheet may be usedas the buffer, and be disposed such that gaps between the inner surfacesof the side plates 1412 of the instep 1410 and the step portion 1423 ofthe foot-sole main body 1421 are filled with the rubber sheet. However,the buffer is not limited to this, and a leaf spring, a sponge, a solidor semi-solid viscous means may also be used.

In addition, the step portion 1423 of the foot sole 1420 and the sideplates 1412 of the instep 1410 which face the step portion 1423 may beadhered to each other in the process of assembling the foot 150 byfilling the gaps between them with an adhesive which shows elasticityand/or viscosity in a cured or solid state. In such a case, foreignmatter can be prevented from entering the gaps.

The another buffer is preferably formed such that the gaps between theinner surfaces of the side plates 1412 of the instep 1410 and the stepportion 1423 of the foot-sole main body 1421 are completely filled sinceforeign matter can be prevented from entering the gaps in such a case.However, the present invention is not limited to this, and a pluralityof buffers may be arranged with gaps therebetween.

The constructions of the foot-sole circuit unit 2200 including memorymeans which stores the foot-sole information and the instep circuit unit2100 including means for reading out the foot-sole information stored inthe memory means are similar to those explained in the above-describedthird construction, and explanations thereof are thus omitted.

As described above, the foot sole 1420 is elastically attached to theinstep 1410 with the buffers 1430 therebetween, so that the foot sole1420 can move slightly along the Z-axis direction and in the X-Y planewithin a range corresponding to the gaps between the step portion 1423of the foot-sole main body 1421 and the inner surfaces of the sideplates 1412 at the open side of the instep 1410. Accordingly, the impacttransmitted to the instep 1410 from the foot sole 1420 during thewalking motion can be reduced. In addition, even when the foot soleinterferes with bumps and depressions on the road surface, they can beeasily avoided.

The screws 1431 and the buffers 1430 correspond to fastening means withvariable fastening conditions according to the present invention, and anamount of movement (relative movement) of the foot sole 1420 relative tothe instep 1410 and the preload applied to the ZMP sensors can bearbitrarily adjusted by changing the depth to which the screws 1431 areinserted. In addition, the movable range of the foot sole 1420 relativeto the instep 1410 in the X-Y plane can be arbitrarily adjusted byadjusting the external shape of the step portion 1423 of the foot-solemain body 1421. Accordingly, the foot can be flexibly adapted to variousstates of road surfaces by adjusting the depth to which the screws 1431are inserted and the external shape of the step portion 1423.

In the above-described examples, an electronic memory (a RAM, a ROM,etc.) is used as the memory means included in the foot (in the main footbodies 1101 and 1201 or the foot soles 1320 and 1420). However, thepresent invention is not limited to this, and various kinds of memorymeans which can store information can be used. For example, visiblyrecognizable marks such as barcodes, matrix codes, characters, symbols,etc., may be displayed on the main foot body or the foot sole and beread by a detection device such as a CCD or the like provided on theankle or the instep. In addition, the memory means may also be such thatinformation is stored in correspondence with the arrangement ofprojections (pins) and is read out by a photo interpreter or amechanical switch. In addition, the memory means may also be such thatinformation is stored magnetically and is read out by a magnetic head ora reed relay.

A fifth example of a connection structure of a leg and a foot and areplacement structure of the foot at an ankle of the legged mobile robotwill be described below with reference to FIGS. 79 and 80. FIGS. 79 and80 are diagrams showing the sectional construction of a foot 150according to a sixth structure and connecting parts between a lower limb(movable leg) 110 and the foot 150, where FIG. 79 shows a state in whichthe foot is removed from an ankle 114 of the lower limb 110 and FIG. 80shows a state in which the foot 150 is attached to a leg-mountedconnecting part 1001.

In the foot 150 according to the above-described first structure, thebottom surface of the main foot body 1101 serves as the ground-contactsurface which comes into contact with the road surface. In comparison,the foot 150 according to the fifth structure includes an instep 1121which is connected to the ankle 114 of the corresponding lower limb 110and a foot sole 1151 which directly comes into contact with the roadsurface, and has a two-part structure in which the foot sole 1121 ismovably attached to the instep 1151.

In addition, a connecting part provided on the instep 1121 of the foot150 at the upper side of the instep 1121 includes aconnection/positioning concavity 1102, a connector 1103 for providingelectrical connection, a container 1104 for accommodating the connector1003, and a connection actuator 1105.

The foot sole 1151 is a rectangular box-shaped member with an open topwhich includes a bottom plate 1152 and upright side plates 1153 whichare formed integrally with the bottom plate 1152 along the peripheralsides of the bottom plate 1152. The top surface of the bottom plate 1152is in contact with the bottom surface of the instep 1121. In addition,the bottom surface of the bottom plate 1152 serves as the foot bottomsurface of the foot 150. The bottom surface of the bottom plate 1152 andouter surfaces of the side plates 1153 are connected to each other withR surfaces (curved surfaces) or smooth curved surfaces.

The internal shape of the side plates 1153 of the foot sole 1151 issimilar to the shape of side surfaces of the instep 1121, but isslightly larger. The side surfaces of the instep 1121 face the innersurfaces of the side plates 1153 of the foot sole 1151 with small gaps(allowances) therebetween. Accordingly, the foot sole 1151 can moverelative to the instep 1121 along the bottom surface of the instep 1121,that is, in an arbitrary direction in the X-Y plane.

The foot sole 1151 is attached to the instep 1121 with a retainingmechanism (not shown) in such a manner that the foot sole 1151 does notfall from the instep 1121 when the corresponding leg is off the roadsurface and the movement of the foot sole 1151 in the X-Y plane is notrestricted. The retaining mechanism preferably has a mechanism foreasily attaching/detaching the foot sole 1151 when the foot sole 1151 isto be replaced.

A buffer (buffer means) 1154 is disposed between the side plates 1153 ofthe foot sole 1151 and the side surfaces of the instep 1121. An endlessrubber sheet, for example is used as the buffer 1154, and is disposedsuch that gaps between the inner surfaces of the side plates 1153 of thefoot sole 1151 and the side surfaces of the instep 1121 are completelyfilled with the rubber sheet. However, the buffer 1154 is not limited tothis, and a leaf spring, a sponge, a solid or semi-solid viscous meansmay also be used.

In addition, the inner surfaces of the side plates 1153 of the foot sole1151 and the side surfaces of the instep 1121 may be adhered to eachother in the process of assembling the foot by filling the gaps betweenthem with an adhesive which shows elasticity and/or viscosity in a curedor solid state. In such a case, foreign matter can be prevented fromentering the gaps, and effects of the retaining mechanism for movablyattaching the foot sole 1151 on the instep 1121 can be obtained withoutusing one.

In the above-described construction, the foot sole 1151 can move withrespect to the instep 1121 in an arbitrary direction along the bottomsurface of the instep 1121. However, the construction may also be suchthat the foot sole 1151 can only move in a specific direction, such asthe X-axis direction or the Y-axis direction. In addition, the buffer1154 is preferably formed such that the gaps between the inner surfacesof the side plates 1153 of the foot sole 1151 and the side surfaces ofthe instep 1121 are completely filled since foreign matter can beprevented from entering the gaps in such a case. However, the presentinvention is not limited to this, and a plurality of buffers may bearranged with gaps therebetween. In addition, the buffer may also beomitted.

A concavity 1111 is formed in the bottom surface of theconnection/positioning concavity 1102 of the instep 1121, and anelectrical circuit substrate 1112 is disposed in the concavity 1111. Theelectrical circuit substrate 1112 may also be disposed at otherpositions on the instep 1121. The electrical circuit substrate 1112includes a foot-sensor processing unit and a power supply unit.

The foot-sensor processing unit is constructed similarly to that shownin FIG. 74, and foot information related to the foot 150 having thetwo-part structure is stored in a ROM included in the foot-sensorprocessing unit.

In addition, sensors including force sensors 406 and an accelerationsensor 407 are also provided on the instep 1121. The force sensors 406are used for detecting pressures in the Z-axis direction, and areprovided on the bottom surface (surface which comes into contact withthe top surface of the foot sole 1151) of the instep 1121, as shown inFIG. 81. The force sensors 406 are used for calculating the ZMP, and aredisposed at four corners on the bottom surface of the instep 1121 in thepresent example.

Each of these force sensors 406 includes a metal diaphragm and fourstrain gauges, and is constructed by forming a bridge circuit with thefour strain gauges and laminating the stain gauges on the metaldiaphragm. When the bottom surface of the instep 1121 is in contact withthe top surface of the foot sole 1151, the amount of deformation (amountof strain) of the above-described metal diaphragm is output as anelectrical signal so that a force applied by the foot sole 1151 in theZ-axis direction at a position where the sensor 406 is disposed can becalculated on the basis of this output. The force sensors 406 are notlimited to this, and those having other constructions may also be used.In addition, the number of force sensors 406 for detecting the ZMP andthe arrangement thereof are also not limited to the descriptions above.

In addition, although not shown in the figure, an acceleration sensorfor detecting accelerations in the X-axis direction and the Y-axisdirection are also mounted on the instep 1121. Although the positions atwhich the acceleration sensor is arranged are not particularly limited,it is disposed in the concavity 1111 in the present example. The outputfrom the acceleration sensor is used for detecting the inclination ofthe road surface with respect to the direction of gravity or thestumbling motion caused by, for example, bumps and depressions on theroad surface.

The sensors 406 and 407 are electrically connected to an A/D converter405 of the foot-sensor processing unit 400 via an operational amplifier(not shown). The gains of the outputs from the sensors 406 and 407 areof course adjusted in advance in accordance with the dynamic range ofthe A/D converter 405.

Although the instep 1121 is connected to the ankle 114 using theactuator 1105 in this example, it may also be connected using a manuallever shown in FIGS. 71 and 72.

Lastly, the process for calculating the ZMP which is performed by thefoot-sensor processing unit 400 will be described below. The ZMPdescribed herein means a point on a floor surface where the moment dueto a reaction force from the floor surface applied to a walking robot iszero.

When the biped walking robot is in a period of single-foot support, aCPU 401 included in the foot-sensor processing unit 400 calculates theZMP of the corresponding foot on the basis of detection values(pressures) obtained from the four sensors 406 provided on the main footbody 1101 or the instep 1121 (hereinafter represented by the main footbody 1101) and information related to the arrangement positions of thesensors 406 (in this case, this information is assumed to be stored inthe ROM 403 as one of the foot sensor information) as follows:$\begin{matrix}{{ZMP} = \frac{\sum\limits_{i = 1}^{4}{{\overset{\rightarrow}{f}}_{i} \cdot {\overset{\rightarrow}{P}}_{i}}}{\sum\limits_{i = 1}^{4}{\overset{\rightarrow}{f}}_{i}}} & (9)\end{matrix}$where,

-   -   {right arrow over (f_(i))}: arrangement position of each force        sensor, and    -   {right arrow over (P_(i))}: force detected.

When the biped walking robot is in a period of two-foot support, twoZMPs are calculated by the foot-sensor processing units 400 of the leftand right feet 150, and the actual ZMP is calculated by the CPU 301included in the main control unit 300 on the basis of the two ZMPs.

The ZMP can be calculated if detection values are obtained from at leastthree force sensors. However, since the ZMP is calculated by detectionvalues obtained by four force sensors, the reliability of the ZMPcalculation is increased. When four force sensors are provided, the ZMPmay be calculated from the outputs of three of the four force sensors,and the output from the remaining force sensor may be used for checkingthe calculated ZMP. Also in this case, the reliability of the ZMPcalculation can be increased.

The number of force sensors provided on the foot is not limited to fouras long as three or more force sensors are provided. When n forcesensors are provided, the ZMP can be calculated as follows:$\begin{matrix}{{ZMP} = \frac{\sum\limits_{i = 1}^{n}{{\overset{\rightarrow}{f}}_{i} \cdot {\overset{\rightarrow}{P}}_{i}}}{\sum\limits_{i = 1}^{n}{\overset{\rightarrow}{f}}_{i}}} & (10)\end{matrix}$where,

-   -   {right arrow over (f_(i))}: arrangement position of each force        sensor, and    -   {right arrow over (P_(i))}: force detected.

The ZMP, which is calculated as described above by the foot-sensorprocessing unit 400, is transmitted to the main control unit 300 via aninput/output controller of the foot-sensor processing unit 400, acommunication cable, and an input/output controller of the main controlunit 300 (none of them is shown in the figure). Then, the CPU 301 of themain control unit 300 calculates command values which are to be suppliedto the actuators 306 on the basis of the ZMP of each foot and otherinformation. Accordingly, the walking motion and other motions of therobot are controlled on the basis of the command values.

The acceleration sensor 407 detects the accelerations of the foot in theX-axis direction and the Y-axis direction. When the foot is placed onthe floor surface, the CPU 401 of the foot-sensor processing unit 400calculates the inclination angle of the foot (the foot bottom surface orthe X-Y plane) relative to the horizontal plane on the basis of theoutput from the acceleration sensor 407. In addition, when the robot isin the period of single-foot support, the amount of impact applied tothe idling leg is calculated or the stumbling motion which occurs whilethe robot walks is detected on the basis of the variation in thedetection value obtained by the acceleration sensor 407.

The above-described information obtained by the foot-sensor processingunit 400 is transmitted to the main control unit 300 along with the ZMPand is used as basic information for controlling each part.

The sensor outputs from the force sensors 406 and acceleration sensor407 are obtained at a constant period, or as necessary, by thefoot-sensor processing unit 400, and the ZMP, the inclination angle ofthe foot, etc., are also calculated at a constant period, or asnecessary.

The main control unit 300 requests the foot-sensor processing unit 400of each foot to transmit the information (calculation results) bypolling at a predetermined period, or as necessary, and then thefoot-sensor processing unit 400 transmits the information to the maincontrol unit 300. Alternatively, the foot-sensor processing unit 400 ofeach foot may also transmit the information to the CPU 301 of the maincontrol unit 300 by interruption. In addition, the information may alsobe transmitted using both of the above-described methods.

In the above-described example, the CPU 401 of the foot-sensorprocessing unit 400 performs predetermined calculations on the basis ofthe outputs obtained by the force sensors 406 for detecting the ZMP andthe acceleration sensor 407, and the calculation results are transmittedto the main control unit 300. Alternatively, however, two CPUs may beprovided, and the calculation of the ZMP and the calculation of theinclination of the foot, etc., may be performed by different CPUs.

In addition, although the foot-sensor processing unit 400 and the maincontrol unit 300 are connected to each other via the input/outputcontrollers and the communication cable, a bus 404 of the foot-sensorprocessing unit 400 and the bus 304 of the main control unit 300 mayalso be directly connected to each other. In addition, when a datatransmitter/receiver for wireless data communication between thefoot-sensor processing unit 400 and the main control unit 300 and/or anelectric power transmitter/receiver for supplying electric power bywireless communication are provided, the cable for connecting thefoot-sensor processing unit 400 and the main control unit 300 can beomitted. Accordingly, the construction can be made simpler and the taskof replacing the foot can be facilitated.

In the above-described example of the present invention, the outputsfrom the sensors 406 and 407 provided on the foot 150 (the main footbody 1101 or the instep 1121) are used by the foot-sensor processingunit 400, which are also provided on the foot 150, for performingpredetermined calculations such as the ZMP calculation regarding thefoot 150, and then the calculation results are transmitted to the maincontrol unit 300 of the robot's main body. Accordingly, the processingload on the main control unit 300 can be reduced and the main controlunit 300 can be dedicated to other calculation processes. As a result,processes with high urgency can be performed with a quick response time.

In addition, since the sensors 406 and 407 provided on the foot 150 areconnected to the foot-sensor processing unit 400 and the foot-sensorprocessing unit 400 is connected to the main control unit 300 with thecommunication cable, wiring in the robot and the construction ofconnectors can be made simpler compared to the case in which the sensors406 and 407 are directly connected to the main control unit 300. Inaddition, when the data is communicated by wireless communication asdescribed above, there is an advantage in that the number ofcommunication channels can be reduced.

In addition, since the distances from the sensors 406 and 407 on thefoot 150 to the foot-sensor processing unit 400 which performs thecalculation processes based on the detection values obtained by thesensors 406 and 407 are extremely small, noise included in the sensoroutputs can be reduced and the accuracy of the processing results can beincreased.

In the fifth structure of the foot 150, since the foot sole 1151 ismovably attached to the instep 1121, a time delay is generated betweenthe motion of the foot sole 1151 and that of the instep 1121 when therobot walks. In addition, since the buffer 1154 is placed between thefoot sole 1151 and the instep 1121, when the idling leg is placed on theroad surface, the reaction force from the road surface is slowly appliedto the lower limb 110. Accordingly, the impact on the joints of thelower limb 110 can be reduced and load on the actuators can also bereduced. In addition, the attitude stability of the robot with respectto fast operations of the actuators which occurs when the robot is movedfast can be improved. In addition, even when there are mechanical errors(displacements) in the driving system or when control errors occur, theymay be absorbed within the movable range of the foot sole 1151 and theirinfluence can be reduced.

In addition, in the fifth structure, when elastic means is used as thebuffer means between the instep 1121 and the foot sole 1151, there is arisk in that the foot sole 1151 will continuously vibrate with respectto the instep 1121 for a long time and the vibration will adverselyaffect the controllability of the walking motion. In such a case,viscous means (for example, a damper) is preferably provided along withthe elastic means in order to improve the damping characteristics. Inthis case, the elasticity coefficient of the elastic member and theviscosity coefficient of the viscous member are preferably set such thatthe vibration of the foot sole 1151 which occurs when the foot sole 1151leaves the road surface in the walking motion of the leg is reduced to apredetermined extent before the foot sole 1151 is placed on the roadsurface again. Since the vibration of the foot sole 1151 is reduced to apredetermined extent at the time when the idling leg is placed on theground, it is not necessary for the robot's control system (thefoot-sensor processing unit 400 or the main control unit 300) tore-perform the trajectory calculation and other calculations forcontrol. Accordingly, the controllability can be improved. Theabove-described predetermined extent refers to a minimum necessaryvibration which can be tolerated while the control system of the robotachieves stable walking motion.

In addition, in the fifth structure, the force sensors 406 for detectingthe ZMP and the acceleration sensor 407 are provided on the instep 1121,and not on the movable foot sole 1151. Accordingly, different from thecase in which the sensors 406 and 407 are provided on the foot sole1151, wires for connecting the sensors 406 and 407 to the foot-sensorprocessing unit 400 do not include moving portions. Therefore, themovement of the foot sole 1151 can be prevented from being impeded bythe wires and the wires can be prevented from being damaged by themovement of the foot sole 1151. In particular, since the sensors 406 fordetecting the ZMP are provided on the bottom surface of the instep 1121(surface which comes into contact with the top surface of the foot sole1151), the sensors 406 for detecting the ZMP receive pressures from thetop surface of the foot sole 1151, which is equivalent to the roadsurface from the point of ZMP detection, and errors in the detectionvalues due to the variation in the state of the road surface can bereduced. Therefore, the ZMP can be detected more accurately.

Appendix

Although the present invention has been described above in detail inconjunction with a particular example, various amendments andmodifications can of course be made by those skilled in the art withinthe scope of the present invention.

The present invention is not limited to products called “robots”, andmay be applied to any kinds of mechanical apparatuses which movesimilarly to human beings by making use of electric or magnetic actions.For example, the present invention may also be applied to toys, etc.,which belong to other industrial fields.

More specifically, the foregoing descriptions merely illustrate thepresent invention, and are not intended to limit the scope of thepresent invention. The substance of the present invention should bedetermined by claims stated at the top.

Industrial Applicability

The present invention provides a foot of a legged mobile robot in whichthe variation in a resistive-force-generation effective surface causedby the variation in the shape of the foot due to the movement of the ZMPis reduced, which is adaptable to various walking surfaces such ascontinuous and discontinuous surfaces, rigid surfaces, viscoelasticsurfaces, etc., and which ensures sufficient attitude stability of therobot.

In addition, the present invention provides a legged mobile robot inwhich the variation in the resistive-force-generation effective surfacecaused by the variation in the shape of the foot due to the movement ofthe ZMP is reduced, which has a foot adaptable to various walkingsurfaces such as continuous and discontinuous surfaces, rigid surfaces,viscoelastic surfaces, etc., and which thereby ensures sufficientattitude stability.

In addition, according to the present invention, variation in theresistive force against the moment about the yaw axis can be reducedirrespective of the position of the ZMP, and the possibility thatso-called spinning motion will occur can be reduced. In addition, motionof the robot controlled by the control system can be predicted and theattitude stability can be improved. In addition, since the plantar-archportion is provided, even when there are bumps and depressions on theroad surface, the possibility that the foot will step on the bumps andfall into a so-called seesaw state can be reduced. In addition, sincethe foot sole as no angular corners (the corners and the side edges areformed by smooth curved surfaces), interference with the road surfacecan be reduced and the stumbling motion can be prevented. Accordingly,the attitude stability of the legged mobile robot can be sufficientlyensured.

In addition, according to the present invention, the attitude andbehavior of the robot when it falls over can be predicted, so thatcontrols related to the falling motion, for example, control to avoidfalling over, control to reduce the impact of falling over, control torecover from falling over, etc., can be easily implemented, and thebreakage of each part due to falling can be prevented.

In addition, according to the present invention, since the foot sole canmove along a plane which is approximately parallel to the foot bottomsurface, even when there are bumps and depressions on the road surfaceand a part of the foot sole interferes with them when the idling leg isplaced on the road surface, the foot sole can move within its movablerange so as to eliminate such interference or absorb the force appliedby the road surface. Accordingly, high-speed motion can be achieved withhigh stability.

In addition, according to the present invention, since memory meanswhich stores the information related to the main foot body or the footsole is provided on the main foot body or the foot sole, the controlsystem of the robot's main body can easily acquire the informationcorresponding to a new foot when an old one is replaced therewith.Accordingly, a workload required when the foot or the foot sole isreplaced can be reduced.

In addition, according to the present invention, since the outputs fromthe sensors provided on each foot (the main foot body or the footinstep) are processed by the foot-mounted processing means provided onthe corresponding foot, it is not necessary for the control means of therobot's main body to perform the calculation processes. Accordingly,processing load placed on the control means can be reduced.

In addition, according to the present invention, the calculation resultsobtained by the foot-mounted processing means provided on each foot aretransmitted to the control means of the robot's main body. Accordingly,compared to the case in which the outputs from the sensors are directlytransmitted to the control means of the robot's main body, complicationof wiring for connecting them can be prevented.

For example, since the ZMP calculation for each foot is performed by thefoot-mounted processing means provided on the corresponding foot (themain foot body or the foot instep), it is not necessary for the controlmeans of the robot's main body to perform these calculations, and theprocessing load placed on the control means can be reduced. In addition,since the calculation results (ZMP) are transmitted from each foot,compared to the case in which the outputs from the sensors are directlytransmitted to the control means of the robot's main body, complicationof the wiring for connecting them can be prevented.

Furthermore, when the foot-mounted processing means can be optimized inaccordance with the relationship with the sensors, and it is notnecessary to change the processes performed by the control means of therobot's main body when the foot is replaced, so that the foot can beeasily replaced.

1. A leg device of a legged mobile robot having a plurality of movablelegs, comprising: a foot sole having a foot bottom surface and sidesurfaces which extend continuously from the periphery of the foot bottomsurface; and a first concavity having a slope which slopes toward theinside of the foot bottom surface.
 2. A leg device of a legged mobilerobot according to claim 1, wherein the ground-contact portion isdisposed at each of four comers of the foot bottom surface.
 3. A legdevice of a legged mobile robot according to claim 1, further comprisinga flexible portion disposed in the first concavity, the flexible portionbeing composed of a material having a predetermined elasticity.
 4. A legdevice of a legged mobile robot according to claim 1, further comprisinga second concavity in the first concavity, the second concavity beingdeeper than the slope of the first concavity.
 5. A leg device of alegged mobile robot according to claim 4, wherein the flexible portionis disposed in the second concavity.
 6. A leg device of a legged mobilerobot according to claim 1, further comprising one or more grooves, eachgroove being formed in a ground-contact surface of the foot such thatthe groove extends from the first concavity across a peripheral portionof the foot and communicates with the outside through one of the sidesurfaces of the foot.
 7. A leg device of a legged mobile robot accordingto claim 1, comprising: an instep attached to the corresponding movableleg; and a foot sole attached to the instep such that the foot sole canmove along a plane parallel to the foot bottom surface.
 8. A leg deviceof a legged mobile robot according to claim 1, comprising: a main footbody which is detachably attached to an end portion of the correspondingmovable leg; and memory means which is provided on the main foot bodyand which stores information related to the main foot body.
 9. A legdevice of a legged mobile robot according to claim 1, comprising: aninstep which is retained by the corresponding movable leg at an ankle ofthe corresponding movable leg; a foot sole detachably attached to theinstep; and memory means which is provided on the foot sole and whichstores information related to the foot and/or control means whichcontrols motion of the corresponding movable leg on the basis of theinformation stored in the memory means.
 10. A leg device of a leggedmobile robot according to claim 1, comprising: a main foot body which isretained by the corresponding movable leg at an ankle of thecorresponding movable leg; memory means which is provided on the mainfoot body and which stores information related to the main foot bodyand/or control means which controls motion of the corresponding movableleg on the basis of the information stored in the memory means; and anopening through which the memory means and/or the control means faceoutside so that the memory means and/or the control means can bereplaced.
 11. A leg device of a legged mobile robot according to claim9, wherein the control means reads out the information stored in thememory means at the time of initialization.
 12. A method for controllinga legged mobile robot having a foot which is detachably attached to anend portion of a movable leg, the method comprising the steps of:storing information related to the foot in memory means provided on thefoot; reading out the information from the memory means at the time ofinitialization; and controlling motion of the movable leg on the basisof the information read out.
 13. A leg device of a legged mobile robotaccording to claim 10, wherein the control means reads out theinformation stored in the memory means at the time of initialization.